c. 1400, "not in agreement, unamiable," from Old French desagreable (13c.), from des- "not, opposite of" (see dis-) + agreable "pleasing; in agreement; consenting" (see agreeable). Meaning "not in accord with one's taste, offensive to the mind or senses" is from 1690s. Related: Disagreeably; disagreeableness. Slightly earlier in same sense was unagreeable (late 14c.). Related: Disagreeability.
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 14c., plesaunte (early 14c. as a surname), "pleasing or acceptable to God;" also "agreeable, desirable; delightful, delicious; satisfying to the mind or senses;" of persons, "charming, gracious," from Old French plaisant "pleasant, pleasing, agreeable" (12c.), present participle of plaisir "to please, give pleasure to, satisfy," from Latin placere "to be acceptable, be liked, be approved" (see please). Pleasantry has the word's modern French sense of "funny, jocular, witty." Related: Pleasantly. Pleasantness "pleasing or agreeable character or quality" is attested from 1520s.