late 14c., "to sing," from Old French chanter "to sing, celebrate" (12c.), from Latin cantare "to sing," originally frequentative of canere "sing" (which it replaced), from PIE root *kan- "to sing."
The frequentative quality of the word was no longer felt in Latin, and by the time French emerged the word had entirely displaced canere. Meaning "to sing as in the church service, in a style between song and recitation" is by 1580s. Related: Chanted; chanting.
1670s, "a song," especially one slow and monotonous, from chant (v.), or else from French chant (12c.), from Latin cantus "song, a singing; bird-song," from past participle stem of canere. Meaning "a Gregorian melody," usually of medieval origin, is from 1789. Meaning "monotonous recitation of words" is from 1815.