befoul (v.)

Old English fulian "to become foul, rot, decay," from ful (see foul (adj.)). Transitive meaning "make foul, pollute" is from c. 1200. Meaning "become entangled" (chiefly nautical) is from 1832, probably from foul (adj.) in the sense "obstructed by anything fixed or attached" (late 15c.). "A term generally used in contrast to clear, and implies entangled, embarrassed or contrary to: e.g. to foul the helm, to find steerage impracticable owing to the rudder becoming entangled with rope or other gear" [Sir Geoffrey Callender, "Sea Passages," 1943]. Related: Fouled; fouling. Hence also foul anchor (1769), one with the slack of the cable twisted round the stock or a fluke; noted by 1832 as naval insignia.

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).