[This entry is taken from a chapter of Part II of the open-source textbook Spanish-English Cognates: An Unconventional Introduction to Spanish Linguistics.]
Other English and Spanish words related to slavery
Eng. manumission ~ Sp. manumisión
Slavery in Rome was not necessarily a life sentence, the way it was in many other societies, whether ancient or more recent. It seems that the freeing of slaves occurred quite regularly in the Roman world, at least for urban slaves, if not so much with rural slaves and those who worked the mines. After a period of, say, 20 years of service, slaves could be freed by their owners.
There were different ways in which the freeing of a slave could take place, but the most common one was for a slave owner to write it in his will. There came to be legal restrictions, however, as to what percentage of one’s slaves could be freed this way. As Mary Beard tells us in her book SPQR: A History of Ancient Rome:
Roman slavery was in some respects as brutal as Roman methods of military conquest. But for many Roman slaves, particularly those working in urban domestic contexts rather than toiling in the fields or mines, it was not necessarily a life sentence. They were regularly given their freedom, or they bought it with cash they had managed to save up; and if their owner was a Roman citizen, then they also gained full Roman citizenship, with almost no disadvantages as against those who were freeborn. The contrast with classical Athens is again striking: there, very few slaves were freed, and those who were certainly did not gain Athenian citizenship in the process, but went into a form of stateless limbo. This practice of emancipation – or manumission, to follow the Latin term – was such a distinctive feature of Roman culture that outsiders at the time remarked upon it and saw it as a powerful factor in Rome’s success. As one king of Macedon observed in the third century BCE, it was in this way that ‘the Romans have enlarged their country’. The scale was so great that some historians reckon that, by the second century CE, the majority of the free citizen population of the city of Rome had slaves somewhere in their ancestry.
The Latin name for the freeing of a slave was mănūmĭssĭo (genitive: mănūmĭssōnis), a noun derived by means of the third declension suffix ‑ĭōn‑(is) from the stem mănūmĭss‑ of the passive participle mănūmĭssus, of the verb mănūmittĕre ‘release, free, emancipate’. This verb was a compound formed of the ablative form manū of the word manus ‘hand’ (root: man‑; cf. Sp. mano ‘hand’), which meant something like ‘from the hand’, plus the verb mĭttĕre that meant ‘to send, let go, send off, etc.’, the source of Spanish meter ‘to put in(to)’ (principal parts: present tense mĭttō, present infinitive mĭttĕre, perfect active mīsī, passive participle mĭssus).
In addition to the literal meaning ‘hand’, the Latin word manus had several figurative senses, one of which was ‘legal power’. More specifically, in legal language, manus could mean ‘the legal power of a husband over his wife, the manus’ (L&S). And although the main meaning of the verb mĭttĕre was ‘to send’, additional sense was ‘to release, let go’, which is the sense that applies here. The fact that this compound contained a conjugated word form, manū, with the ablative inflection ‑ū, not just the root man‑, shows that this compound word was derived from the contraction of a phrase, cf. mănū mittĕre, which literally meant something like ‘to release by the legal power’, and was thus not formed as a regular compound word (which would have been *măn‑ĭ‑mittĕre). This phrase is not attested in Latin, but a similar one is, namely manū ēmittĕre, which contains the verb ēmĭttĕre instead of mĭttĕre, the former being derived from the latter by the prefix ē‑ which was a variant of the prefix ex‑ ‘out’ (Lat. ēmĭttĕre is the source of the loanword cognates Eng. emit ~ Sp. emitir. In addition to meaning ‘the freeing of a slave, manumission’, Lat. mănūmissĭo had a secondary sense, namely ‘a remission of punishment, pardon’ (L&S).
English and Spanish have borrowed this Latin word, resulting in the cognates Eng. manumission ~ Sp. manumisión. Eng. manumission [ˌmænjəˈmɪʃən] was borrowed in the middle of the 15th century, either from Latin or French, or both. Fr. manumission is attested in the early 14th century, a loan from Latin, and it was used to refer to legal freeing of Roman slaves, but also of feudal serfs, cf. Modern French manumission, pronounced [manymiˈsjɔ̃]. From around the same time (early 14th century) is the patrimonial French version of this Latin noun, namely mainmise, a synonym of manumission derived from the verb mainmettre, the French version of the Latin verb mănūmittĕre (see below).
Eng. manumission’s original meaning was just as in the original, ‘the action of manumitting a slave; the fact of being manumitted; formal release from slavery or servitude; an act or instance of this’ (OED). However, as the OED tells us, this word is now historical and it is used to refer just to the freeing of Roman slaves, not of slaves in other historical contexts. As we will see below, the word for freeing of slaves in modern times goes by another name, namely Eng. emancipation ~ Sp. emancipación ~ Fr. émancipation (also affranchissement).
We mentioned that the Latin noun mănūmissĭo is derived from the verb mănūmittĕre ‘to legally release, free, emancipate’. This Latin verb has also been borrowed by English and Spanish, cf. Eng. manumit ~ Sp. manumitir, though the verbs are even less common than the nouns. Eng. manumit [ˌmænjəˈmɪt] was first used in the middle of the 15th century, much like the noun. The verb is also now used with a historical meaning, to refer to the freeing of Roman slaves (OED says: ‘Now chiefly historical’). Sp. manumitir is quite a late loanword, from as late as the 18th century perhaps. Other Romance languages, however, borrowed this verb even earlier than English, e.g. Italian manomettere (late 13th century) and French manumettre ‘to set free’ (1338; cf. Middle French manumitter or manumiter) (OED). Thus, although English is said to have borrowed this word directly from (written) Latin, it is quite likely that this loan was facilitated by the existence of the loans in Romance languages, especially French. Modern French does not have a descendant of these verbs anymore, but it has a patrimonial or actualized version of it, namely mainmettre [mɛ̃mɛtʀ], formed from the noun main ‘hand’ and the verb mettre, the patrimonial version of Lat. mĭttĕre and cognate of Sp. meter. Derived from the participle of this verb is the noun mainmise, which, as we saw earlier, is the French equivalent of Eng. manumission.
As we saw, both Sp. manumisión and manumitir are loanwords and there are no patrimonial Spanish words related to them. Catalan, however, has a patrimonial word derived from the verb mănūmittĕre, namely marmesor, which meant ‘executor’, the person charged by a testator or a judge to carry out the provisions of a will and testament. The word marmesor is derived from Lat. mănūmĭssor (genitive: mănūmĭssōris, regular stem: mănū‑mĭss‑ōr‑), a post-classical agent noun meaning ‘one who gives a slave his freedom, a liberator, emancipator’ (L&S), derived by means of the agent suffix ‑ōr‑ from the stem mănūmĭss‑ of the passive participle mănūmĭssus of the verb mănūmĭttĕre (same stem as the noun mănū‑mĭss‑ĭōn‑). This was the name given in Latin to the executor of a will in which faithful slaves or servants were freed. DCEH tells us that the Murcian variety of Spanish borrowed the word marmesor from Catalan in the 14th century. In Modern Standard Spanish, however, the word for ‘executor’ is albacea, which is a loanword from Andalusian Arabic صَحْب الوَصِيَّة (ṣáḥb alwaṣíyya), lit. ‘companion of the will’, cf. Arabic صَحْب (ṣaḥb) ‘companions’ and وَصِيَّة (waṣiyya) ‘will, bequest’. A less common synonym of Sp. albacea is testamentario/a.
 Beard, Mary. 2015. SPQR: a history of ancient Rome. New York: Liveright Publishing Corporation. See also: Thomas E. J. Wiedemann. 1985. “The Regularity of Manumission at Rome.” The Classical Quarterly, 35(1), 162-175 (http://www.jstor.org/stable/638813 ) and Marcus Sidonius Falx, J. P. Toner, and Mary Beard. 2014. The Roman guide to slave management: a treatise by nobleman Marcus Sidonius Falx. New York: Overlook Press.