Yours, Etc.: Origins and Uses of 8 Sign-Offs
early 13c., "attempt to clear (someone) from blame," from Old French escuser (12c., Modern French excuser) "apologize, make excuses; pardon, exonerate," from Latin excusare "excuse, make an excuse for, release from a charge," from ex- "out, away" (see ex-) + 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. Excuse me as a mild apology or statement of polite disagreement is from c.1600.
late 14c., "action of offering an apology," from Old French excuse, from excuser (see excuse (v.)). The sense of "that serves as a reason for being excused" is recorded from late 15c.
A version or example of: He's a rotten excuse for a lawyer (1940s+)