Eng. quash and squash, and Sp. casar and concuasar
As we saw earlier, the English verb quash, pronounced [ˈkʰwɒʃ] or [ˈkʰwɑʃ], depending on the dialect, is a 13th century loanword from an Old French verb that was attested with different spellings, among them quaisser, quaissier, quasier, and quassier (OED). The reflex of this verb in Modern French is casser, meaning ‘to break’, as we mentioned earlier. We find different spellings for this verb in Middle English, such as cwesse, queysse, quasche, quassch, quassh, and quaysch. The Old French verb seems to descend from a Vulgar Latin variant *quassiare of classical Latin quăssāre, the same Latin verb that has supposedly given us Sp. quejar, as we saw in the preceding section.
The verb quash has two quite different main meanings in Modern English:
(1) ‘to put down or suppress forcibly and completely’ (AHD), which is applied to things such as revolts, as in quash a rebellion; this sense can be translated into Spanish as sofocar, aplastar, or acallar; and
(2) ‘to set aside or annul, especially by judicial action’ (AHD), which is a legal term, e.g. The High Court later quashed his conviction for murder (LDCE); this sense of quash translates into Spanish as anular, invalidar, or revocar
It is thought that the reason there are two such rather different meanings for Eng. quash is that the these meanings actually come ultimately from two different Latin verbs which merged at some point in Medieval Latin, before the word was borrowed into English or even French. Only one of these meanings, the ‘suppress’ sense, would descend from classical Lat. quassāre, whereas the ‘cancel’ sense presumably comes from a post-classical Lat. cassāre, which merged with quassāre in Medieval Latin and from there made it into Old French. This Latin verb cassāre originally meant ‘to bring to naught, destroy’ and in the language of jurists, ‘to annul, make null or void’ (synonymous with abrogāre; L&S). This verb is attested in the 4th century with the sense ‘to destroy’, in the 5th century with the sense ‘to annul’, and by the 12th century with the sense ‘to reject’ (OED). The original Latin verb cassāre was derived from the classical Latin adjective cassus/a/um ‘null, empty, hollow, etc.’, a word that has not been passed on to most Romance languages (cass‑us > cass‑āre).
The Latin verb cassāre has been borrowed by Spanish, though it is a rare legal term. Portuguese also borrowed the Latin verb, as cassar. This Spanish verb is casar, which is homophonous and homonymous with the verb casar a transitive verb that means ‘to marry’ (the intransitive meaning ‘to get married’ is given by the pronominal or reflexive casarse). The meaning of this legal verb casar is simply ‘to quash’, which the DLE defines by means of some synonyms: ‘anular, abrogar, derogar’ (cf. Eng. annul, abrogate, derogate). María Moliner’s dictionary is more explicit and tells us that this verb is typically used to describe the annulment of a court’s sentence by a higher court.
María Moliner’s dictionary also tells us that the verb casar that means ‘to quash’ used to have a synonym, now obsolete, namely concuasar, a loanword from Lat. conquassāre, a verb derived from the verb quassāre by means of the intensive prefix con‑ (con‑quass‑āre) and which meant ‘to shake severely’ and ‘to shatter, dash to pieces’ (L&S). The obsolete Spanish verb concuasar does not appear in many Spanish dictionaries since it is now obsolete. It does appear in the DLE and MM dictionaries and, interestingly, only María Moliner’s tells us that this verb had the ‘annul’ sense (like casar), now obsolete. Both dictionaries tell us that concuasar used to have a ‘smash, break’ sense (like in the Latin source). In addition, María Moliner’s dictionary tells us about the obsolete ‘annul’ sense. The Academies’ dictionary tells us that in Bolivia concuasar is still used in Bolivia to this day as a transitive verb with the meaning ‘to match up, fit together’, which is curiously a derived sense of the other, unrelated verb casar that means ‘to marry’, according to the Academies’ dictionary (DLE). The Diccionario de americanismos (DA) differs somewhat with this claim and tells us that concuasar is an intransitive verb used in Perú, Bolivia and Paraguay to mean ‘to match, adjust or square one thing with another’ and in Bolivia to mean ‘for two or more people agree on something that has been said or done’.
Most dictionaries treat the two senses of the English verb quash as just two senses of the very same word, a single verb quash. However, at least one major dictionary, the American Heritage Dictionary, gives two different homonymous verbs side by side because of their different ultimate sources. Thus, if we look for the word quash in this dictionary, we find the entries quash1 and quash2.
In addition to borrowing the French descendant of the Latin verb cassāre, English also borrowed a Latin noun derived from this verb, namely the late Latin action noun cassātĭōn‑, derived by means of the suffix ‑ĭōn‑ from the stem cassa‑t‑ of the verb’s passive participle cassātus (cass‑ā‑t‑ĭōn‑). This noun is not attested in classical Latin, so it may have been formed in Medieval Latin or even in French after this language borrowed the Latin verb.
The noun cassation was borrowed into both English and French in the early 15th century. The OED says that Eng. cassation, pronounced [kæˈseɪ̯ʃən] or [kəˈseɪ̯ʃən], came into English from Latin, but it is quite likely that it was formed in French first and from there it passed on to English. The meaning of these words was ‘the action of making null or void; cancellation, abrogation’ (OED). The cognate word casación is attested in Spanish with the same meaning, also by the end of the 15th century, and it probably also came through French. The noun is found in collocations such as recurso de casación ‘appeal in a high court’, tribunal de casación ‘court of cassation’.
The OED tells us that the noun cassation was also used with another sense in the 17th century, a sense that is now obsolete: ‘dismissal of a soldier; cashiering’ (OED). Interestingly, English has another noun cassation, one that means ‘a piece of instrumental music of the eighteenth century similar to the serenade, and often performed out of doors’ (OED), a ‘minor musical genre related to the serenade and divertimento’ (WP). This is a 19th century loan from German kassation, a term used since the second half of the 18th century for a ‘loosely assembled sets of short movements intended for outdoor performance by orchestral or chamber ensembles’, a genre that ‘was popular in southern German-speaking lands’ (WP). The origin for the musical sense of this word has been said to be Italian cassazione, for example by the OED, but this is by no means certain.
English has another verb that is ultimately related to Lat. quassāre, namely one derived in Vulgar Latin from this verb by means of the prefix ex‑, i.e. *exquassāre. This verb made it into Old French as esquasser (also escasser) or esquacer (also escacier) (cognate with Italian squassare). English borrowed this verb from French resulting in Modern English squash, pronounced [ˈskwɒʃ], [ˈskwɔʃ], or [skwɑʃ], depending on the dialect. This verb has two major meanings, each one with additional subsenses (COED):
(1) ‘crush or squeeze (something) so that it becomes flat, soft, or out of shape; squeeze or force into a restricted space’ = Sp. aplastar, chafar, espachurrar; and
(2) ‘suppress or subdue; firmly reject (an idea or suggestion); silence (someone), typically with a humiliating remark’ = Sp. acallar, aplastar, etc.
From the verb squash a homonymous noun was created in English. Its most basic meanings are ‘the act or sound of squashing’ and ‘the fact or condition of being squashed’ (AHD). This noun is more common in British English and its Spanish translations would be: apiñamiento, agolpamiento, apretujón, or apretón.
The noun squash has also been the name of a sport since around 1900, namely ‘a racket game played in a closed walled court with a rubber ball’ (AHD). The sport’s name is derived from the name of the soft, rubber ball used in this racket game, squash ball, and it is an ellipsis for (British) squash rackets or (US) squash tennis (OED). Spanish has borrowed this English word for the name of the sport without any changes or adaptations: squash. The DLE advises us that this word should be pronounced ‘[eskuás]’ (according to María Moliner’s dictionary, it should be ‘[escuásh]’). Finally, let us mention that in Great Britain, the same noun squash is also the name of ‘a citrus-based soft drink’ (AHD). The OED tells us that since the late 19th century, this has been a short form for the compound lemon-squash.
Finally, note that this verb squash and the nouns derived from it are totally unrelated to the homophonous noun squash that means ‘a gourd with flesh that can be cooked and eaten as a vegetable’, as well as ‘the plant which produces squashes. [Several species and varieties of the genus Cucurbita.]’ (COED). This noun squash is a loanword from the Native American Narragansett language asquutasquash, borrowed in the 17th century, which is derived from the root asq that means ‘raw, uncooked’ and meant something like ‘vegetable eating green/raw’. The vegetable name translates into Spanish as calabaza.
 The original says: ‘Derecho Particularmente, anular un *tribunal una *↘sentencia dada por otro. ⇒ Concuasar’ (MM).
 In María Moliner’s dictionary, the original says: ‘concuasar 1. (ant.) tr. Hacer pedazos ↘algo con un golpe. ≃ *Romper. 2. (ant.) Casar (*anular)’ (MM), and in the Academies’ dictionary: ‘concuasar 1. tr. Bol. casar (ǁ corresponder una cosa con otra). 2. ant. Quebrantar, estrellar, hacer pedazos’ (DLE).
 The original says: ‘concuasar. I. 1. intr. Pe, Bo, Py. Coincidir, ajustarse o cuadrarse una cosa con otra. 2. Bo. Coincidir dos o más personas en algo que se ha dicho o hecho’ (DA).
 The OED also tells us that there was a ‘Court of Cassation [French Cour de cassation], in France, the appellation of the supreme court of appeal, as having the power in the last resort to alter, or cancel, or quash (casser) decisions of the other courts which are wrong in form or law’ (OED)
 Wikipedia has a good summary of the speculations that have been made about the origin of the German term kassation: ‘The etymology of the musical term is uncertain. Mozart’s cassations K. 63 and K. 99 open with marches, and the term has been speculatively linked to the Italian word cassa, meaning “drum”. Hermann Abert was among those who thought that the term derives from the Italian cassare, meaning “to dismiss”, implying a musical farewell, or Abschiedsmusik. The French word casser (to break) was also invoked, based on the notion that the movements could be freely broken up into any order. A more likely derivation, reflecting the outdoor character of the genre, involves a transformation of the Austrian dialectal word gassatim: specifically, gassatim gehen was an expression commonly used by local eighteenth-century musicians to refer to street performance’ (WP).