Comments:Владимирцов 160, АПиПЯЯ 27, 284. A Turk.-Mong. isogloss. Mong. *u-su can be explained as a normal dissimilation < *su-su ( < *sub-su); cf. similar cases in *sisegeji > *isegeji 'felt', *sü(t)-sü > *ü-sü 'milk', *sus- > *us- 'disappear, perish'. The relationship of the Mong. and Turk. forms is strengthened by the presence in Turkic of archaic derivatives *sɨb-sɨ-, *sɨb-sa-.