Proto-MSA

*wṭb - to beat, to tan (JL 294)

Arabic
nṭb - to box someone’s ears (LA 1 900)

A variant root?

Arabic
waṭb- - skin in which milk is put; large breast (BK 2 1561; Lane 2949; LA 1 941)
Mehri
wəṭáwb - to tan leather (ML 433)
Jibbali
eṭɔ́b - to tan leather (JL 294)
Soqotri
ö́ṭab - to beat (also about leather in the tanning process) (LS 57; CSOL II 397)