Merriam-Webster's Collegiate® Dictionary, 11th Edition
PLEDGE
I. noun see: plight
Date: 14th century
1. a bailment of a chattel as security for a debt or other obligation without involving transfer of title, the chattel so delivered, the contract incidental to such a bailment,
2. the state of being held as a security or guaranty, something given as security for the performance of an act, a token, sign, or earnest of something else, a gage of battle, toast 3,
6. a binding promise or agreement to do or forbear, b. a promise to join a fraternity, sorority, or secret society, a person who has so promised,
II. transitive verb (pledged; pledging)
Date: 15th century
to make a pledge of, to drink to the health of, to bind by a pledge, to promise the performance of by a pledge, pledger or pledgor noun