What does "pledge" mean?

Additional senses

1. 2.A hypothecation without transfer of possession.
2. 3.Anything given or considered as a security for the performance of an act; a guarantee; as, mutual interest is the best pledge for the performance of treaties. "That voice, their liveliest pledge of hope." Milton.
3. 4.A promise or agreement by which one binds one's self to do, or to refrain from doing, something; especially, a solemn promise in writing to refrain from using intoxicating liquors or the like; as, to sign the pledge; the mayor had made no pledges.
4. 5.A sentiment to which assent is given by drinking one's health; a toast; a health. Dead pledge. Etym: [A translation of LL. mortuum vadium.] (Law) A mortgage. See Mortgage. -- Living pledge. Etym: [A translation of LL. vivum vadium.] (Law) The conveyance of an estate to another for money borrowed, to be held by him until the debt is paid out of the rents and profits. -- To hold in pledge, to keep as security. -- To put in pledge, to pawn; to give as security.
5. 6.To deposit, as a chattel, in pledge or pawn; to leave in possession of another as security; as, to pledge one's watch.
6. 7.To give or pass as a security; to guarantee; to engage; to plight; as, to pledge one's word and honor. We mutually pledge to each other our lives, our fortunes, and our sacred honor. The Declaration of Independence.
7. 8.To secure performance of, as by a pledge. [Obs.] To pledge my vow, I give my hand. Shak.
8. 9.To bind or engage by promise or declaration; to engage solemnly; as, to pledge one's self.
9. 10.To invite another to drink, by drinking of the cup first, and then handing it to him, as a pledge of good will; hence, to drink the health of; to toast. Pledge me, my friend, and drink till thou be'st wise. Cowley.