etymology (n.) Look up etymology at Dictionary.com
late 14c., ethimolegia "facts of the origin and development of a word," from Old French etimologie, ethimologie (14c., Modern French étymologie), from Latin etymologia, from Greek etymologia "analysis of a word to find its true origin," properly "study of the true sense (of a word)," with -logia "study of, a speaking of" (see -logy) + etymon "true sense," neuter of etymos "true, real, actual," related to eteos "true," which perhaps is cognate with Sanskrit satyah, Gothic sunjis, Old English soð "true."

Latinized by Cicero as veriloquium. In classical times, with reference to meanings; later, to histories. Classical etymologists, Christian and pagan, based their explanations on allegory and guesswork, lacking historical records as well as the scientific method to analyze them, and the discipline fell into disrepute that lasted a millennium. Flaubert ["Dictionary of Received Ideas"] wrote that the general view was that etymology was "the easiest thing in the world with the help of Latin and a little ingenuity."

As a modern branch of linguistic science treating of the origin and evolution of words, from 1640s. As "account of the particular history of a word" from mid-15c. Related: Etymological; etymologically.