To make a solemn promise or commitment to do something. She pledged to donate a portion of her salary to charity every month.
To formally promise to give or do something, often as a guarantee or assurance. The company pledged to reduce its carbon emissions by 50% over the next decade.
To bind or commit someone to a promise or agreement. He pledged his friend to secrecy about the surprise party.
To offer something as security for a loan or obligation. He pledged his car as collateral for the bank loan.
To accept (someone) as a prospective member of a fraternity or sorority. The sorority pledged thirty new students during rush week.
(Archaic) To drink to the health of (a person); to toast. The guests pledged the victorious captain with goblets of wine.