Origin and history of befog

1540s, "thick, obscuring mist near the earth's surface," usually produced by cooling of the air below the dew-point, a back-formation from foggy (which appeared about the same time) or directly from a Scandinavian source akin to Danish fog "spray, shower, snowdrift," Old Norse fjuk "drifting snow storm." Compare also Old English fuht, Dutch vocht, German Feucht "damp, moist."

The figurative phrase in a fog "at a loss what to do, in a state of mental obscurity," attested by c. 1600. Automobile fog-lights is from 1962.

Beyond the difference in the place of origin there is really little or no distinction to be drawn between a fog and a cloud. A fog is a cloud resting on the earth ; a cloud is a fog floating high in the air. [T.H. Huxley, "Physiography," 1878]

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 (bygones, bystander); in bylaw it is a different word.

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 words, many of them useful or tuneful, most obsolete, among them bethwack "to thrash soundly" (1550s) and betongue "to assail in speech, to scold" (1630s). Shakespeare's wolf behowls the moon.