early 14c., "sound other than a vowel," from Latin consonantem (nominative consonans), present participle of consonare "to sound together, sound aloud," from com- "with" (see com-) + sonare "to sound" (see sonata). Consonants were thought of as sounds that are only produced together with vowels.

early 15c., from Old French consonant (13c.), from Latin consonantem (nominative consonans), present participle of consonare (see consonant, n.).