Abarim Publications' online Biblical Greek Dictionary
The adverb αχρι (achri), or αχρις (achris) before a vowel, expresses duration or length up onto a specified point in space or time: until or as far as. Combined with the genitive case it means during: until [the passing of] a season/day/period.
Our adverb occurs 50 times in the New Testament; see full concordance. It has no derivations.