dissatisfy 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).

early 15c., satisfien, "do penance," also "appease, assuage;" also "fulfill (a desire), comply with (a command), satiate (a hunger or thirst)," from Old French satisfiier "pay, repay, make reparation" (14c., Modern French satisfaire), from Latin satisfacere "discharge fully, comply with, make amends," literally "do enough."

This is from satis "enough" (from PIE root *sa- "to satisfy") + facere "to make, do, perform" (from PIE root *dhe- "to set, put").

From mid-15c. as "make amends, pay damages."  The meaning "cause to have enough, supply the needs of" is by c. 1500. Of feelings, "meet or fulfill the wish, desire, or expectation of," late 15c. (Caxton). From 1510s as "assure or free from doubt or uncertainty, furnish with sufficient proof." The intransitive sense of "give satisfaction or contentment" is from c. 1600.