late 14c., "particular mode of pronunciation," from Old French acent "accent" (13c.), from Latin accentus "song added to speech," from ad "to" (see ad-) + cantus "a singing," past participle of canere "to sing" (from PIE root *kan- "to sing").
The Latin word was a loan-translation of Greek prosōidia, from pros- "to" + ōidē "song," which apparently described the pitch scheme in Greek verse.
The meaning "effort in utterance making one syllable stronger than another in pitch or stress" is attested from 1580s; as "mark or character used in writing to indicate accent," it is recorded by 1590s. The decorative-arts sense of "something that emphasizes or highlights" is from 1972.
The soundest distinction perhaps is that "accent" refers to the habitual stress laid on a syllable in ordinary pronunciation ; "stress" to a syllable specially accented for this or that reason, logical, rhetorical, or prosodic purely. [George Saintsbury, "Historical Manual of English Prosody," 1914]