excuse v.

word-forming element, in English meaning usually "out of, from," but also "upwards, completely, deprive of, without," and "former;" from Latin ex "out of, from within; from which time, since; according to; in regard to," from PIE *eghs "out" (source also of Gaulish ex-, Old Irish ess-, Old Church Slavonic izu, Russian iz). In some cases also from Greek cognate ex, ek. PIE *eghs had comparative form *eks-tero and superlative *eks-t(e)r-emo-. Often reduced to e- before -b-, -d-, -g-, consonantal -i-, -l-, -m-, -n-, -v- (as in elude, emerge, evaporate, etc.).

c. 1200, "reason or motive for a decision, grounds for action; motive," from Old French cause "cause, reason; lawsuit, case in law" (12c.), and directly from Latin causa "a cause; a reason; interest; judicial process, lawsuit," which is of unknown origin.

From mid-14c. as "cause of an effect; source, origin." From late 14c. as "that which affords opportunity for a cause to operate, occasion;" also "reason for something taking place or for something being so; rational explanation." Also late 14c. as "proper or adequate reason, justification for an action." The sense of "matter of interest or concern; a side taken in controversy" is from c. 1300. Cause célèbre "celebrated legal case" is 1763, from French. Common cause "a shared object or aim" is by 1620s.