Comments: Short vowel reconstructed because of reduction in Bacbi. Ing. aχka = Chech. äχka 'in summer' (Chech. äχkē is a suffixed form).
The meaning "summer" is obviously secondary. The older meaning 'year' is still preserved in the PN compound *sṭā-χḳŭ 'last year' > Chech. stoχka, Ing. sɔχk, Bacb. sṭaŭχḳŭ (for the etymology of the first part see PEC *śwăjV).