word-forming element of verbs and nouns from verbs, with a wide range of meaning: "about, around; thoroughly, completely; to make, cause, seem; to provide with; at, on, to, for;" from Old English be- "about, around, on all sides" (the unstressed form of bi "by;" see by (prep.)). The form has remained by- in stressed positions and in some more modern formations (bylaw, bygones, bystander).
The Old English prefix also was used to make transitive verbs and as a privative prefix (as in behead). The sense "on all sides, all about" naturally grew to include intensive uses (as in bespatter "spatter about," therefore "spatter very much," besprinkle, etc.). Be- also can be causative, or have just about any sense required. The prefix was productive 16c.-17c. in forming useful words, many of which have not survived, such as bethwack "to thrash soundly" (1550s) and betongue "to assail in speech, to scold" (1630s).
late 14c., dauben, "to smear with soft, adhesive matter, to plaster or whitewash a wall" (Dauber as a surname is recorded from mid-13c.), from Old French dauber "to whitewash, plaster" (13c.), perhaps from Latin dealbare, from de-, here probably meaning "thoroughly," + albare "to whiten," from albus "white" (see alb).
From 1590s as "to dress or adorn (a person) without style or taste." Painting sense is from 1620s. Related: Daubed; daubing, daubery. As a noun from mid-15c. as "daubing material, cheap kind of mortar;" 1761 as "inartistic painting."