To forgive; to pardon.
I excused him his transgressions.
To allow to leave, or release from any obligation.
I excused myself from the proceedings to think over what I'd heard.
To provide an excuse for; to explain, with the aim of alleviating guilt or negative judgement.
You know he shouldn't have done it, so don't try to excuse his behavior!
To relieve of an imputation by apology or defense; to make apology for as not seriously evil; to ask pardon or indulgence for.