early 14c., "alphabetic element other than a vowel," from Latin consonantem (nominative consonans) "sounding together, agreeing," as a noun, "a consonant" (consonantem littera), present participle of consonare "to sound together, sound aloud," from assimilated form of com "with, together" (see con-) + sonare "to sound, make a noise" (from PIE root *swen- "to sound").

Consonants were thought of as sounds that are produced only together with vowels. Related: Consonantal.

early 15c., "agreeing, corresponding, harmonious," from Old French consonant (13c.) and directly from Latin consonantem (nominative consonans) "sounding together, agreeing," present participle of consonare "to sound together, sound aloud," from assimilated form of com "with, together" (see con-) + sonare "to sound, make a noise" (from PIE root *swen- "to sound").

Of music, c. 1600; of words, 1640s. Related: Consonantly.