Notes: Correspondences are regular, and the etymology seems quite reliable. The original meaning is certainly 'winter'; the meaning 'summer' in PN comes from the intermediate stage 'year' (cf. the meanings in Tsezian languages).
See Trubetzkoy 1922,241 (for EC). Abdokov (1983, 91) proposes a different comparison for EC: PWC *bž́V 'winter, autumn', which seems impossible for phonetic reasons.