Origin and history of discussion

the modern English word is a merger of two words, both in Middle English as quashen, from two unrelated Latin verbs.

1. "to suppress, overcome" (mid-13c.); "to make void, annul, nullify, veto" (mid-14c.), from Old French quasser, quassier, casser "to annul, declare void," and directly from Medieval Latin quassare, alteration of Late Latin cassare, from cassus "null, void, empty" (according to Watkins from extended form of PIE root *kes- "to cut"). The meaning "subdue, put down summarily" is from c. 1600.

2. "to break, crush, beat to pieces" early 14c., from Old French quasser, casser "to break, smash, destroy; maltreat, injure, harm, weaken," from Latin quassare "to shatter, shake or toss violently," frequentative of quatere (past participle quassus) "to shake." According to Watkins this is from PIE root *kwet- "to shake" (source also of Greek passein "to sprinkle," Lithuanian kutėti "to shake up," Old Saxon skuddian "to move violently," German schütteln "to shake," Old English scudan "to hasten").

In Medieval Latin, quassare often was used for cassare, and in later French the form of both words is casser. The words in English now are somewhat, or entirely, fused. Related: Quashed; quashing.

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).