fˀm - IV. to widen; to fill a vessel; to become full of fat
(Lane 2326)
Arabic
fiˀām- - a thing which is spread to sit upon or to lie upon
(Lane 2326)
Probably related to Akk. piyāmu ‘a textile’, Gez. fāˀm ‘woof, spun yarn, opening of a tunic’, Tgn. faˀmi ‘the thread which is in the shuttle while weaving; thread for making the wool; weft’.
Can be compared to *piˀ(-at-), but the meaning shift is not entirely clear. [Nöldeke 152] translated it as ‘troop, new army’ with a remark: «Originally there was probably something like ‘attack frontage’».