consonant (adj.)

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

consonant (n.)

early 14c., "sound other than a vowel," from Latin consonantem (nominative consonans), present participle of consonare "to sound together, sound aloud," from com "with, together" (see com-) + sonare "to sound, make a noise," "to sound," from PIE *swene-, from root *swen- "to sound" (see sound (n.1)). Consonants were thought of as sounds that are only produced together with vowels.