Pledge, earnest, token, pawn, hostage are comparable when they denote something that is given or held as a sign of another’s faith or intention to do what has been promised.
Pledge, originally and still in some applications a technical legal term, applies in general to something handed over to another as a token <bear her this jewel, pledge of my affection —Shak. > or as security for the performance of an obligation or payment of a debt.
Earnest, basically the money or other thing of value given by a buyer to a seller to bind a bargain, in its extended sense applies to something which serves as a promise or assurance of more to come or which establishes a strong probability of it.
Token (see also SIGN 1 ) applies to something given as a guaranty or proof of a person or thing’s authority, authenticity, or good faith.
In specific concrete use token is applied to something which serves as a proof of an obligation, a right, a debt, or a payment; thus, a coinlike piece of metal sold by a transportation company for use as a ticket is usually called a token; coins or notes issued by some countries, states, or cities as currency at a nominal or face value above their real value but redeemable at their face value are collectively called tokens. Pawn retains in anthropological use an earlier broad equivalence to a security pledge and then applies to a person held in servitude pending settlement of a debt.
In more general use pawn specifically refers to a personal chattel deposited as security for the money loaned on it by another, usually by a person called a pawnbroker whose business is the loaning of money on such security. In extended use pawn often carries a suggestion of something held for a time and liable to redemption or withdrawal by the actual owner.
Hostage basically applies to a person handed over to another or kept by another as a guarantee of one’s good or peaceable or submissive intentions or as a pledge until one’s agreement or promise has been fulfilled. But sometimes the term is extended to other guarantees and pledges.