1894 (Havelock Ellis), from Latin fellatio, noun of action from fellatus, past participle of fellare "to suck," from suffixed form of PIE root *dhe(i)- "to suck." The sexual partner performing fellatio is a fellator; if female, a fellatrice or fellatrix. L.C. Smithers' 1884 translation from German of Forberg's "Manual of Classical Erotology" has fellator, fellatrix, and fellation, but not fellatio.
word-forming element attached to verbs, making nouns of state, condition, or action, from French -ion or directly from Latin -ionem (nominative -io, genitive -ionis), common suffix forming abstract nouns from verbs.
<a href="https://www.etymonline.com/word/fellation">Etymology of fellation by etymonline</a>
Harper, D. (n.d.). Etymology of fellation. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/fellation