early 13c., "to clear (someone) from blame," from O.Fr. escuser
, from L. excusare
"release from a charge," from ex-
"out, away" + causa
"accusation, legal action" (see cause
). Meaning "to obtain exemption or release" is from mid-15c.; that of "to accept another's plea of excuse" is from early 14c. The noun sense of "that which is offered as a reason for being excused" is recorded from c.1500. Excuse me
as a mild apology or statement of polite disagreement is from c.1600.