c.1300, dabben "to strike," of unknown origin, perhaps imitative. Modern sense of "strike with a slight, quick pressure" developed by mid-16c., influenced by French dauber (see daub). Related: Dabbed; dabbing. As a noun from c.1300, "heavy blow with a weapon." Dab hand is British slang, 1828, from dab "expert" (1690s), said to be school slang, of unknown origin, perhaps from dab in the "strike lightly" sense.
An expert; a skilled person; an adept: He is reportedly a dab hand at setting lofty prices
[1828+ British; fr late 1600s dab, ''an expert,'' of unknown origin]