pledge 
(plĕj)
(plĕj)n.
1. A solemn binding promise to do, give, or refrain from doing something: signed a pledge never to reveal the secret; a pledge of money to a charity.
2.
a. Something given or held as security to guarantee payment of a debt or fulfillment of an obligation.
b. The condition of something thus given or held: put an article in pledge.
3. Law
a. Delivery of goods or personal property as security for a debt or obligation: a loan requiring a pledge of property.
b. The contract or transaction stipulating or involving such delivery.
4. A token or sign: "fair pledges of a fruitful tree" (Robert Herrick).
5. A person who has been accepted for membership in a fraternity or similar organization and has promised to join but has not yet been initiated.
6. A vow to abstain from alcoholic liquor: ex-drinkers who have taken the pledge.
7. Archaic The act of drinking in honor of someone; a toast.
v. pledged, pledg·ing, pledg·es
v.tr.
1. To offer or guarantee by a solemn binding promise: pledge loyalty to a nation; pledge that the duties of the office will be fulfilled. See Synonyms at promise.
2. To bind or secure by a pledge or promise: pledged themselves to the cause. See Synonyms at devote.
3. To deposit as security; pawn.
4.
a. To promise to join (a fraternity or similar organization).
b. To accept as a prospective member of such an organization.
5. Archaic To drink a toast to.
v.intr.
1. To make a solemn binding promise; swear.
2. Archaic To drink a toast.
[Middle English, from Old French plege, probably from Late Latin plevium, a security, of Germanic origin; see dlegh- in the Appendix of Indo-European roots.]