No definitive etymology can be suggested. May be related to PWS *pas- ‘part, lot’, assuming that the Akkadian word originally designated a specially fashioned piece of stone used as a lot.
Akkadian
passuku - to remove, to clear away
(CAD P 536, AHw. 839)
Only the Assyrian D and Dt forms attested. No definitive etymology can be suggested.
Akkadian
pāsū - viscera(?), (interior) part(s)(?)
(CAD P 225, AHw. 839)
Var. pasuntu, pasumtu. An eventual connection with pasāmu ‘to cover up, to veiľ looks probable both semantically and formally (Black 1983:33 ad l. 22).
Derived words: puṣādu ‘cut (of meat)’ (CAD P 538, AHw. 883). A direct cognate is Arb. fṣd ‘to cut, to slit, to open a vein’. Syr. pṣidā ‘fons’ undoubtedly goes back to the same root with a feasible semantic development.
Probably to be compared with WS *pṣ̂ṣ̂ ‘to split, to break’.
As an alternative, Arb. fṣṣ ‘to separate, to remove, to displace’ can be considered. Cf. also Nab. pṣṣ ‘to be divided’, an Arabism according to DNWSI 931.