Varro, On the Latin Language, V 2-3
“…The first part, where we consider why and from where words develop, The Greeks call etymology; the second part is semantics. I will speak of these two categories in the following books together but more sparingly of the second.
These things are often rather obscure because every word that has been used does not still exist; the charge of time has made some forgotten. Moreover, every word that still exists, since it may be subject to misuse (applied incorrectly, for example) may not be wholly the same (since many words are altered by changes in spelling). And not every word has its origin from roots based in our own language. Many words indicate a different thing now from what they used to mean: for example, hostis (“enemy”). For, people who used this word in the past meant a foreigner who followed his own native laws; now when they use it they mean what used to be called perduellem (“enemy”).”
priorem illam partem, ubi cur et unde sint verba scrutantur, Graeci vocant etymologian, illam alteram peri semainomenon. De quibus duabus rebus in his libris promiscue dicam, sed exilius de posteriore.
Quae ideo sunt obscuriora, quod neque omnis impositio verborum exstat, quod vetustas quasdam delevit, nec quae exstat sine mendo omnis imposita, nec quae recte est imposita, cuncta manet (multa enim verba litteris commutatis sunt interpolata), neque omnis origo est nostrae linguae e vernaculis verbis, et multa verba aliud nunc ostendunt, aliud ante significabant, ut hostis: nam tum eo verbo dicebant peregrinum qui suis legibus uteretur, nunc dicunt eum quem tum dicebant perduellem.