Lat. avert- and avers-
Latin āvĕrtĕre ‘to turn away, aside’ was formed with the prefix ā‑ or ab‑ ‘away from’ added to the verb vĕrtĕre. This has resulted in the English verb to avert, which came into English in the 14th century from Old French avertir, which was identical to the verb avertir we just saw that descended from Lat. advĕrtĕre. The French verb has not made it into Modern French, perhaps because it was homonymous with the verb derived from advĕrtĕre.
English avert is a fancy, literary word that has two main senses: (1) ‘turn away (one’s eyes or thoughts)’ and (2) ‘prevent or ward off (an undesirable occurrence)’. Latin āvĕrtĕre has left no reflexes in Spanish, that is, Spanish has no cognates of English avert. English avert translates into Spanish primarily as evitar ‘avoid’, apartar ‘to move away’, or even prevenir ‘to prevent’, as in: to avert one’s eyes = apartar la vista and to avert disaster = evitar el desastre. In French too, Eng. avert translates as prévenir or éviter in the ‘prevent’ sense and as détourner in the sense of ‘turn aside (eyes, thoughts)’.
The past participle of Lat. āvĕrtĕre was āvĕrsus (ā+vĕrs+us), which has given us the English adjective averse [ə.ˈvɜɹs], that means ‘having a feeling of opposition, distaste, or aversion; strongly disinclined’ (AHD), a 16th century borrowing directly from Latin, as in I am averse to taking risks. The closest translations for this word in Spanish are reacio, as in Soy reacio a tomar riesgos ‘I am risk-averse’ or opuesto, as in Estoy opuesto al riesgo ‘I am averse to risk’.
In Latin, the stem of the participle āvĕrsus, namely āvĕrs‑, could be turned into a noun by means of the ending ‑iōn‑ mentioned earlier, giving us the Latin noun āversiōnem (nominative: āversiō), meaning literally ‘turning away’ and, figuratively, ‘loathing, abhorrence’. It has resulted in the fancy cognate nouns Eng. aversion [ə.ˈvɜɹ.ʒən] and Sp. aversión [a.βeɾ.ˈsi̯on], with pretty much the same meaning. The English noun aversion used to mean ‘the act of turning away from an object’ in English but that meaning is now obsolete. Its meaning is ‘a strong dislike of something or someone’ (DOCE), a synonym of hatred. This word is found in the phrase aversion therapy, which is ‘a type of behavior therapy designed to make patients give up a habit by causing them to associate it with an unpleasant effect’ (COED). This type of psychotherapy dates from 1946. Its name in Spanish is calqued from the English one, namely terapia de aversión.
Another prefix that was often used to derive Latin verbs was ob‑, meaning ‘towards’ and, not surprisingly, Latin did have a verb obvĕrtĕre meaning ‘to turn towards’. This verb has given us the very fancy English verb obvert, used mostly in philosophical logic with the sense of ‘alter (a proposition) so as to infer another proposition with a contradictory predicate’ (COED). Spanish has not borrowed this verb, however, and thus has no cognate for this rare English word.
The past participle of obvĕrtĕre was, of course, obvĕrsus. This has given us Eng. obverse, which is a fancy word that can be used as an adjective or noun. The English adjective obverse can mean ‘facing or turned toward the observer’ (AHD), when talking of a coin or a statue, or a situation or feeling, for instance. It can also mean ‘serving as a counterpart or complement’ (AHD). As a noun, it is used to refer to ‘The side of a coin, medal, or badge that bears the principal stamp or design’ and to ‘the more conspicuous of two possible alternatives, cases, or sides’, as in the obverse of this issue (AHD). In Logic, the obverse is ‘the counterpart of a proposition obtained by exchanging the affirmative for the negative quality of the whole proposition and then negating the predicate’, so that the obverse of Every act is predictable is No act is unpredictable (AHD).
The Spanish equivalent of obverse in logic is simply (lo) contrario. When talking about coins and other such two-sided objects is anverso, a word that was borrowed from French and whose etymon is Lat. inversus (see above). Latin inversus gave us Old French enverse (Mod.Fr. envers [ɑ̃.ˈvɛʀ]), which at one point was borrowed by Spanish as anverso, used to refer to the opposite of reverse when speaking of things such as coins, a technical term equivalent to Eng. obverse.
Despite the obvious similarity, the English adjective overt ‘done or shown openly’ is unrelated to the English verb obvert. Eng. overt is an early 14th century loanword from Old French overt, past participle of ovrir ‘to open’, from Vulgar Latin *ōperīre, from Lat. aperīre ‘to open’ (the initial o came from the influence of Latin cōperīre ‘to cover’). The Modern French of these words are infinitive ouvrir ‘to open’ and participle/adjective ouvert ‘open(ed)’. These words are cognates of Sp. abrir ‘to open’ and Sp. abierto ‘opened; open’. Eng. overt translates into Spanish as manifiesto/a, declarado, evidente, explícito, claro, palpable, aparente, or patente when it means ‘obvious’, as in overt hostility, and as abierto/a, when it means ‘deliberate’, as in overt criticism.
Finally, Latin had a noun derived from obvĕrtĕre, namely obvĕrsĭo, derived from the passive participle stem obvers‑ and the noun suffix ‑iōn‑ and meaning ‘a turning towards, offering’. English borrowed this noun too to go along with the verb to obvert. The meaning of this very fancy and rare word is ‘an act or instance of obverting’, ‘something that is obverted’. In logic, it refers to ‘a form of inference in which a negative proposition is obtained from an affirmative, or vice versa’ (RHWU).