Comment: The Rut., Kryz., Bud. and Ud. forms are historical plurals (with -Vr and -uχ). The Archi form is also a result of a secondary reinterpretation of the form *jam (< *ʔIam:) as a plural; a new singular form *ja had been built and later yielded (quite regularly) Arch. oj. Note that an analogous thing happened also in Udi, where there exists a noun i 'hearing' (and the verb i-baksun 'to hear').The old "plural" form (but already refigured according to the singular) is preserved in Arch. ojom 'ears'.
See Лексика 1971, 126; Гигинейшвили 1977, 116; Талибов 1980, 274.