late 14c., "pleasing combination of sounds, harmony," from Old French consonance (12c.) "consonance, rhyme" and directly from Latin consonantia "harmony, agreement," from consonantem (nominative consonans) "agreeing in sound," present participle of consonare "to sound together, sound aloud" (see consonant (adj.)).
From early 15c. as "agreement among persons as to facts or opinions." Meaning "accord or agreement of sounds in words or syllables" is from 1580s.