>the fact that <udan> is the sole surviving member of its paradigm in
Indo-Aryan.
>Pokorny also gives G. udnás and pl. udá: (< *udo:r). Are those forms
>only given by the grammarians?
Udan is "defective in the strong cases".
"Of a:s 'mouth' and ud 'water' only a case or two are found."
"The neuter stems asan 'blood', yakan 'liver' ... a:san 'mouth', udan
'water' ... are required to make their nom-acc-voc in all numbers from the
parallel stems asrj, yakrt, .. a:sya, udaka.. which are fully inflected."
There are also compound forms of ud- listed in Pokorny, and a few not
listed, eg a whole bunch beginning with uda- (my Skt dictionary gives over
50 such compounds), and the adjective udrin = abounding in waters (Rg Veda).
Peter