Other forms: dabs
To dab is to touch something lightly and repeatedly with something soft. Blotting a spill, patting a cut with cotton wool.
The movement is gentle and repeated, which is what separates it from rubbing: you dab at a stain rather than scrubbing it. It takes at for what you are working on and on for what you are applying. As a noun a dab is a small amount — a dab of glue, a dab of butter. British English also keeps a dab hand, meaning somebody unexpectedly good at something.
Middle English
dabben — to strike
English, today
dab
From Middle English dabben (“to strike”), probably of gmq - origin, related to Old Icelandic dabba (“to tap, slap”), perhaps ultimately imitative of the sound. Compare also with Middle Dutch dabben (“to pinch, knead, fumble, dabble”) (Dutch dabben (“(of a horse) to stamp with the forelegs”)), Dutch deppen (“to dab”), possibly German tappen (“to fumble, grope”). The noun is from Middle English dabbe (“a strike, blow”), from the verb. Related to tap. Compare also drub, dub. African-American sense of “playful box” perhaps influenced by dap (“fistbump”).
Etymology from Wiktionary, CC BY-SA