COMMENT: Cf. also Hurr. eššǝ 'horse', see Diakonoff-Starostin 1986, 34. The first (weak) syllable with the initial laryngeal was dropped in Av., Lak. and Khin. (and, of course, in PWC where it is the normal reflex), but is preserved in PD and PL. Medial -r- in PD does not represent the original *-n- (which was probably dropped); it is rather a trace of an oblique stem *ʔurči < *ʔuč-ri-.
One of the most secure common NC roots. See Чарая 1912, 48-49; Trubetzkoy 1930, 277; Балкаров 1964, 97; Шагиров 1977, 2, 141, Abdokov 1983, 124. Charaya notes also Kartvelian parallels: Georg. aču,ači 'interjection (addressing a horse)', ačua '(child.) horse' - most probably NC loanwords (cf. analogous loans of *jǝ̄mcō 'ox'). Abdokov (loc. cit.) suggests also an etymological connection of the root with *=ăč_wV 'to bring, carry' (q.v.), but there are phonetic problems with this solution.