dissertation (n.)

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).

Proto-Indo-European root meaning "to line up."

It forms all or part of: assert; assertion; assort; consort; desert (v.) "to leave one's duty;" desertion; dissertation; ensorcell; exert; exsert; insert; seriatim; seriation; series; sermon; serried; sorcerer; sorcery; sort.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit sarat- "thread;" Greek eirein "to fasten together in rows;" Latin serere "to join, link, bind together," series "row, chain, series, sequence, succession;" Gothic sarwa (plural) "armor, arms;" Old Norse sörve "necklace of stringed pearls;" Old Irish sernaid "he joins together;" Welsh ystret "a row."