Merriam-Webster's Collegiate® Dictionary, 11th Edition
EXCUSE
I. transitive verb (excused; excusing)
Etymology: Middle English, from Anglo-French escuser, excuser, from Latin excusare, from ex- + causa cause, explanation
Date: 13th century
1. to make apology for, to try to remove blame from, to forgive entirely or disregard as of trivial import ; regard as excusable ,
3. to grant exemption or release to , to allow to leave , to serve as excuse for ; justify , excusable adjective excusableness noun excusably adverb excuser noun Synonyms: see: excuse
II. noun
Date: 14th century
the act of excusing,
2. something offered as justification or as grounds for being excused, an expression of regret for failure to do something, a note of explanation of an absence, justification , reason , see: apology