dessert 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).

late 12c., serven, "to render habitual obedience to, owe allegiance to," also "minister, give aid, give help," from Old French servir "to do duty toward, show devotion to; set table, serve at table; offer, provide with," from Latin servire "be a servant, be in service, be enslaved;" figuratively "be devoted; be governed by; comply with; conform; flatter," originally "be a slave," related to servus "slave," which is of uncertain origin.

Perhaps from Etruscan (compare Etruscan proper names Servi, Serve, Latinized as Servius), but de Vaan says it is from Proto-Italic *serwo- "shepherd," *serwā- "observation," from PIE *seruo- "guardian" (source also of Avestan haraiti "heeds, protects"):

Rix 1994a argues that the original meaning of *serwo- probably was 'guard, shepherd', which underwent a pejorative development to 'slave' in Italy between 700 and 450 BC. Servire would be the direct derivative of servus, hence 'be a slave'; servare would in his view be derived from an older noun *serwa- or *serwom 'observation, heedance'.

It is attested by c. 1200 in widespread senses: "to be in the service of, perform a service for; attend or wait upon, be personal servant to; be a slave; owe allegiance to; officiate at Mass or other religious rites;" from early 13c. as "set food at table;" mid-14c. as "to wait on (customers)."

From late 14c. as "treat (someone or something) in some fashion." To serve (someone) right "treat as he deserves" is recorded from 1580s. Sense of "be useful, be beneficial, be suitable for a purpose or function" is from early 14c.; that of "take the place or meet the needs of, be equal to the task" is from late 14c.; that of "suffice" is from mid-15c.

The meaning "render active military service" is from 1510s. The sporting sense is attested by 1580s, first in tennis. The legal sense of "present" (a writ, warrant, etc.), "give legal notice of" is from early 15c. To serve hand and foot "minister to attentively" is by c. 1300.

He no schuld neuer wond

To seruen him fro fot to hond

["Amis and Amiloun," c. 1330]