collateral — Collateral is money or property which is used as a guarantee that someone will repay a loan.
bond — A bond between people is a strong feeling of friendship, love, or shared beliefs and experiences that unites them.
deed — A deed is something that is done, especially something that is very good or very bad.
guarantee — a promise or assurance, especially one in writing, that something is of specified quality, content, benefit, etc., or that it will perform satisfactorily for a given length of time: a money-back guarantee.
insurance — the act, system, or business of providing financial protection for property, life, health, etc, against specified contingencies, such as death, loss, or damage, and involving payment of regular premiums in return for a policy guaranteeing such protection
pledge — a solemn promise or agreement to do or refrain from doing something: a pledge of aid; a pledge not to wage war.
security — freedom from danger, risk, etc.; safety.
