The noun ετος (etos) means year (Matthew 9:20, Luke 3:1, John 2:20). This word comes from the ancient Proto-Indo-European root "ut", meaning year. The adverb of time περυσι (perusi), meaning last year, also makes use of this ancient root, as do the Sanskrit word for year, vatsa, and the Hittite one: whitish. And since longer periods of time are commonly expressed in years, the Latin word veteranus, from whence comes the English "veteran", makes use of the same root.

Our noun ετος (etos) is used 49 times in the New Testament, see full concordance, and also occurs in the New Testament as part of the following compounds:

The curious noun ενιαυτος (eniautos) also means year, or more precise: anniversary (a word that comes from the Latin word for year, namely annus, plus the verb verto, to turn or return). Our noun combines the common preposition εν (en), meaning in, at, on, with the familiar pronoun αυτος (autos), meaning self.

In the classics this noun is often used as synonym of ετος (etos), meaning year (see above), but because it doesn't actually speak of any particular length of time, merely the fact that we've gone full circle, it also became used to signify a return or completion of much greater cycles (up to 600 years). It is used 14 times in the New Testament; see full concordance.