The n. is a vn. of harraba, vb. II, properly ‘to help to escape; to force to flee, put to flight; to liberate, free (a prisoner); to rescue (a distrained or impounded thing; jur.)’, but then also applied to non-human objects and used with the extended meaning of ‘to traffic, smuggle’. Morphologically a D-stem with caus. meaning, *‘to let/make escape (sc. goods)’.
Cf. also ►muharrib, n., illicit dealer, trafficker; smuggler: PA II, restricted to [v2] of corresponding vb. ►muharrab, pl. ‑āt, n.pl., smuggled goods, contraband: PP II, [v2].