Comment: Cf. also Ud. ap:e-sun 'to become ripe, boiled', p:ap:-sun (Vart. bap:-sun) 'to be in time', Vart. b-ap:i ( = Nidzh. p:ap:i) 'ripe'. The Udi forms clearly point to PL labialised *q̇ʷ and distinguish this root clearly from PL *ʔirq̇är 'to come, reach' (Ud. ej-sun / e-sun). Medial -r- regularly gets lost in verbal roots of all the languages that have preserved PL *ʔi(r)q̇ʷV.
An old derivate from this root (with reduction of the initial syllable) may be Tab. q̇abi (Düb. q̇awi) 'old' (cf. an analogous development in Dargwa).