Presumably derived from PS *yad- ‘hand’. According to Leslau, Amh. and Hrs. forms, as well as Gez. adverb waˀəda/waˀda/wəˀda contain the deictic element w- (CDG 602).
Direct identification with PS *ˀalp- ‘head of large cattle,’ taken for granted in Fox 2003:74, is semantically difficult. An eventual connection with Arb. ˀlf is worth considering (Kogan 2015: 71)
PWS
*ˀaly-at- - fat tail (of a certain race of sheep)
(SED I No. 5)