Notes: One of very widely spread common NC roots. Correspondences are quite regular (Nakh *p- reflects labialisation, while *sṭ is a result of the following -j-). There may have existed an early variant *ćĭwo (or *ćĭwjo) which would account for Nakh forms without *p- (*sṭ-aḳ) and the PWC absence of labialisation.
A possible HU parallel is *-s(u)wa in Hurr. tar-ž(u)wa-nnǝ, Urart. tar-šua-nǝ 'man, human being' (where *tar- is probably connected with *tur- 'male', see *lɨwŁV); see Diakonoff-Starostin 1986, 39.