Both phonetically and semantically the EC-WC parallel seems quite plausible. PWC has a frequent labial prefix. In a position following a labial WC labialized consonants usually are delabialized, but not in this case (PAA *ś : PAK *ś point unambiguously to *śʷ; in Ubykh, in fact, delabialisation had occurred - otherwise we would have pšʷa- - but this is a regular later Ubykh process). Lack of delabialisation can be very well explained if we assume a form like *pǝ-śǝHwV > *pǝ-śǝwV (not *pǝ-śʷV) for the early period, when the after-labial delabialisation process was active. For phonetic reasons it seems better to keep apart WC *pǝsV 'soul' (which is superficially closer to PN *sa), which has a quite different NC etymology (see under *ʡăms_a).

    The semantic developments 'to breathe' > 'get tired' and 'get tired' > 'die' are quite usual (cf. also the meanings of the corresponding root in EC).