1) n. property pledged to secure a loan or debt, usually funds or personal property as distinguished from real property (but technically collateral can include real estate). 2) adj. referring to something that is going on at the same time parallel to the main issue in a lawsuit or controversy which may affect the outcome of the case, such as adoption of a new federal regulation or a criminal trial of one of the parties. Example: John has filed a lawsuit in New Mexico, where he lives, to establish that he is not the father of Betty's child, while Betty has filed for divorce in Colorado asking that John pay child support for the child. The New Mexico paternity suit is collateral to the Colorado divorce action.