disagree (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).

late 14c., "to give consent, assent," from Old French agreer "to please, satisfy; to receive with favor, take pleasure in" (12c.), a contraction of phrase a gré "favorably, of good will," literally "to (one's) liking" (or a like contraction in Medieval Latin) from a, from Latin ad "to" (see ad-) + Old French gre, gret "that which pleases," from Latin gratum, neuter of gratus "pleasing, welcome, agreeable" (from suffixed form of PIE root *gwere- (2) "to favor").

In Middle English also "to please, gratify, satisfy," a sense preserved in agreeable. Of parties, "come to agreement; make a settlement," mid-15c.; meaning "to be in harmony in opinions" is from late 15c. Of things, "to coincide," from 1520s. To agree to differ is from 1785 (also agree to disagree, 1792). Related: Agreed; agreeing.

late 15c., "refusal to agree or assent," from disagree + -ment. From 1570s as "difference in form or essence," also "difference of opinion or sentiments," perhaps a separate formation from dis- + agreement. From 1580s as "a falling out, contention." As "unsuitableness, unfitness," by 1702.