PAK *ʡa; Ub. def. á-q̇aṗa. For the etymology of -ṗa see *ṗA; the root q̇a- is discoverable in many compounds (q̇a-(n)cʷá 'finger' etc.). External correspondences suggest that this root must have been labialised, but labialisation was for some reason lost in PWC. Indeed, we find the labialised form *q̇́Iʷa (~*q:́Iʷa) within the compound *q̇́Iʷa-(p)ƛ̣a (~*q:́Iʷ-) 'arms, embrace; to embrace' q.v.
AT parallels for this root suggested by several authors are not persuasive (see Шагиров 2, 154 - 155 with literature).