etymology

First recorded in 1350–1400; Middle English, from Latin etymologia, from Greek etymología, equivalent to etymológ(os) “studying the true meanings and values of words” (étymo(s) “true” + lógos “word, reason”) + -ia noun suffix; see etymon, -y³

English etymology comes via Old French etimologie, ethimologie from Latin etymologia (which Cicero spells in Greek letters and glosses as veriloquium, Latin for “speaking the truth, conveying the truth”), a loan translation of the Greek etymología “analysis of a word to discover its true meaning.” Etymología is a compound of the neuter noun étymon “true meaning of a word according to its origin” (a neuter noun use of the adjective étymos “true”) and -logía, a Greek combining form used in forming the names of sciences or bodies of knowledge.
Ancient and medieval etymologies are mostly conjectures, puns, or folk etymologies, and are generally wildly incorrect. Cicero, for instance, gives the etymology of Venus (stem Vener- ), the goddess of love, as a derivation of the verb venīre “to come” because love and desire come to all. The most famous etymological howler in Latin is Lūcus a nōn lūcendō “Grove from there being no light,” a pun on lūcus “a clearing, grove” and lūcēre “to shine.” Lūcus a nōn lūcendō first appears in a commentary on the Aeneid by Maurus Servius Honoratus, a grammarian of the late 4th and early 5th centuries.
Common English folk etymologies include cockroach for Spanish cucaracha and chaise lounge for the correct chaise longue. In the case of cockroach, you have the unfamiliar Spanish sounds assimilating with two near-sounding English words, cock and roach. The longue in chaise longue means “long,” but to English readers, looks very close in spelling to lounge, which is a logical use for a chair that is made for reclining on.
Etymology in the sense “the linguistic science that investigates the origins of a word, its relationships with words in other languages, and its historical development in form and meaning” dates from the 1640s.

C14: via Latin from Greek etumologia; see etymon, -logy