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 prosoidia, from pros- "to" + oide "song," which apparently described the pitch scheme in Greek verse. Meaning "effort in utterance making one syllable stronger than another in pitch or stress" is from 1580s; as "mark or character used in writing to indicate accent," 1590s. The decorative-arts sense of "something that emphasizes or highlights" is from 1972.