debug v.

active word-forming element in English and in many verbs inherited from French and Latin, from Latin de "down, down from, from, off; concerning" (see de), also used as a prefix in Latin, usually meaning "down, off, away, from among, down from," but also "down to the bottom, totally" hence "completely" (intensive or completive), which is its sense in many English words.

As a Latin prefix it also had the function of undoing or reversing a verb's action, and hence it came to be used as a pure privative — "not, do the opposite of, undo" — which is its primary function as a living prefix in English, as in defrost (1895), defuse (1943), de-escalate (1964), etc. In some cases, a reduced form of dis-.

"insect, beetle," 1620s (earliest reference is to bedbugs), of unknown origin, probably (but not certainly) from or influenced by Middle English bugge "something frightening, scarecrow" (late 14c.), a word or meaning that has become obsolete since the "insect" sense arose, except in bugbear (1570s) and bugaboo (q.v.).

The Middle English word probably is connected with Scottish bogill "goblin, bugbear," or obsolete Welsh bwg "ghost, goblin" (compare Welsh bwgwl "threat," earlier "fear," Middle Irish bocanách "supernatural being"). Some speculate that these words are from a root meaning "goat" (see buck (n.1)) and represent originally a goat-like specter. Compare also bogey (n.1) and Puck. Middle English Compendium compares Low German bögge, böggel-mann "goblin." The sense shift perhaps was by influence of Old English -budda, used in compounds for "beetle" (compare Low German budde "louse, grub," Middle Low German buddech "thick, swollen").

The name of bug is given in a secondary sense to insects considered as an object of disgust and horror, and in modern English is appropriated to the noisome inhabitants of our beds, but in America is used as the general appellation of the beetle tribe .... A similar application of the word signifying an object dread to creeping things is very common. [Hensleigh Wedgwood, "A Dictionary of English Etymology," 1859]

The meaning "defect in a machine" (1889) may have been coined c. 1878 by Thomas Edison (perhaps with the notion of an insect getting into the works). In compounds, the meaning "person obsessed by an idea" (as in firebug "arsonist") is from 1841, perhaps from notion of persistence. The colloquial sense of "microbe, germ" is from 1919.

Bugs "crazy" is from c. 1900. Bug juice as a slang name for drink is from 1869, originally "bad whiskey." The 1811 slang dictionary has bug-hunter "an upholsterer." Bug-word "word or words meant to irritate and vex" is from 1560s.