disturb v.

word-forming element of Latin origin meaning 1. "lack of, not" (as in dishonest); 2. "opposite of, do the opposite of" (as in disallow); 3. "apart, away" (as in discard), from Old French des- or directly from Latin dis- "apart, asunder, in a different direction, between," figuratively "not, un-," also "exceedingly, utterly." Assimilated as dif- before -f- and to di- before most voiced consonants.

The Latin prefix is from PIE *dis- "apart, asunder" (source also of Old English te-, Old Saxon ti-, Old High German ze-, German zer-). The PIE root is a secondary form of *dwis- and thus is related to Latin bis "twice" (originally *dvis) and to duo, on notion of "two ways, in twain" (hence "apart, asunder").

In classical Latin, dis- paralleled de- and had much the same meaning, but in Late Latin dis- came to be the favored form and this passed into Old French as des-, the form used for compound words formed in Old French, where it increasingly had a privative sense ("not"). In English, many of these words eventually were altered back to dis-, while in French many have been altered back to de-. The usual confusion prevails.

As a living prefix in English, it reverses or negatives what it is affixed to. Sometimes, as in Italian, it is reduced to s- (as in spend, splay, sport, sdain for disdain, and the surnames Spencer and Spence).

"muddy, foul with extraneous matter, thick, not clear," used of liquids having the lees disturbed or colors, 1620s, from Latin turbidus "muddy, full of confusion," from turbare "to confuse, bewilder," from turba "turmoil, crowd," which is of uncertain origin. De Vaan writes:

Turba seems most similar to [Greek syrbe, Attic tyrbe] 'noise, commotion', ... which are probably loanwords. In that case, Latin would have borrowed the word from a Greek dialect, or both Greek and Latin borrowed it from a third source. In view of the quite well-developed word family already in Plautus, which suggests that turba had been in the language for some time, the latter option seems preferable.

Related: Turbidly; turbidness.

1590s, "agitated, put out of a settled state or regular order," past-participle adjective from disturb. Meaning "emotionally or mentally unstable" is from 1904.