c. 1300, confusioun, "overthrow, ruin," from Old French confusion "disorder, confusion, shame" (11c.) and directly from Latin confusionem (nominative confusio) "a mingling, mixing, blending; confusion, disorder," noun of action from past-participle stem of confundere "to pour together," also "to confuse" (see confound).
Meaning "act of mingling together two or more things or notions properly separate" is from mid-14c. Sense of "a putting to shame, perturbation of the mind" (a sort of mental "overthrow") is from c. 1400 in English, while that of "mental perplexity, state of having indistinct ideas" is from 1590s. Meaning "state of being mixed together," literally or figuratively, "a disorderly mingling" is from late 14c.