One wonders whether PWS *wṣb/*nṣb ‘to stand, to be erect; to be firm, stable’ may be further related as variant roots.
Cf. *ŝaḥm- "fat", level?
From Aramaic this root was borrowed into Akkadian as sapāḳu ‘to be sufficient’.
Separated from Sem. *špl 'to be low' for phonetic reasons.