Comment: The Ag. form stems from the Burk. dialect, thus ṭaw < *ṭab < *ṭaṗ. The original *-p is preserved in Tsakh.; all other languages reflect a secondary variant *ṭaṗ(an) with assimilated *ṗ. A form withoutsuffixes is reflected in Lezg., Rut. and Ag.; other languages either reflect a form with a common suffix *-an (Tsakh., Kryz., Ud.) or the original plural form *ṭap-ar (Tab., cf. also Lezg. daṗar / ṭaṗar 'lock', Lezg. Khl. ṭaṗar id.). Cf., perhaps, also Tsakh. ṭopi 'jug, jar' (with a secondary vowel labialisation) = Ud. t:op:i id.
The Ud. form t:ap:an may have been borrowed from Arm. tapan (all the Lezg. forms with -an are derived from this source by Vinogradova-Klimov 1979, 157); however, it is less probable for Kryz. and Tsakh. - and in general, considering the lack of IE etymology of the Armenian word, it seems much more probable that Arm. tapan was itself borrowed from a Caucasian source.