early 13c., "to satisfy a debt" (either for oneself or on behalf of another), from O.Fr. acquitter "settle a claim," from à "to" + quite "free, clear" (see quit). Meanings "set free from charges" and "to discharge one's duty" both recorded from late 14c.
"freed, exonerated," 1670s, pp. adj. from acquit (q.v.). Formerly in this sense was acquit (late 14c.), perhaps on analogy of pps. such as hit.