A Collateral

1. (finance) A security or guarantee (usually an asset) pledged for the repayment of a loan if one cannot procure enough funds to repay.

Synonym: pledge

2. (now rare, genealogy) A collateral (not linear) family member.
3. (anatomy) A branch of a bodily part or system of organs.
4. (marketing) Printed materials or content of electronic media used to enhance sales of products (short form of collateral material).
5. (anatomy) A thinner blood vessel providing an alternate route to blood flow in case the main vessel becomes occluded.
6. (archaic) A contemporary or rival.