From hdyn with elision of final n and intervocalic ḏ. DJBA posits a separate lemma of identical shape used with feminine nouns supposedly rather from h)dy, but it seems to us that gender neutral usage of a single form is more likely. If correct, though, then it must be seen as the equivalent of hhyˀ pron. : "that one" (f.) rather than "this".
In TgJon-tosephta, non-core LJLA only as a rare Babylonianism