Comments: PAT *č̣ʷa (cf. also Abaz. Ashkh. f̣a). PAK *ṗʡʷa-č̣́á. Only the second part of the PAK word corresponds to PAT *č̣ʷa and Ub. ṗc̣a (this peculiar correspondence - note that this is the only word with it, and likewise the only word in PAT with *č̣ʷ and in Abaz. with f̣!- points unambiguously to the PWC lateral *ƛ̣́ʷ). The first component is not quite clear (perhaps it's PAK *ṗʡʷa 'place' - 'having thin places'?).
PAK *-č̣́a is contained also in *psǝ-n-č̣́á 'light', *za-n-č̣́á 'straight' (originally *'light and thin', 'straight and thin').