From convertō +‎ -tiō.

conversiō f (genitive conversiōnis); third declension

1. the act of turning round or revolving; revolution
2. (medicine) the act of inverting
3. alteration, change; conversion
4. the repetition of the same word at the end of a clause
5. (Ecclesiastical Latin) conversion

Third-declension noun.

• “conversio”, in Charlton T. Lewis and Charles Short (1879), A Latin Dictionary, Oxford: Clarendon Press
• “conversio”, in Charlton T. Lewis (1891), An Elementary Latin Dictionary, New York: Harper & Brothers
• "conversio", in Charles du Fresne du Cange, Glossarium Mediæ et Infimæ Latinitatis (augmented edition with additions by D. P. Carpenterius, Adelungius and others, edited by Léopold Favre, 1883–1887)
• “conversio”, in Gaffiot, Félix (1934), Dictionnaire illustré latin-français, Hachette.
• Carl Meißner; Henry William Auden (1894), Latin Phrase-Book‎^[1], London: Macmillan and Co.
  • the process of translation: interpretatio, translatio (not versio or conversio)
    
  • revolution: conversio rei publicae (Div. 2. 2. 6)