1. Situated or running side by side; parallel.
2. Coinciding in tendency or effect; concomitant or accompanying.
3. Serving to support or corroborate: collateral evidence.
4. Of a secondary nature; subordinate: collateral target damage from a bombing run.
5. Of, relating to, or guaranteed by a security pledged against the performance of an obligation: a collateral loan.
6. Having an ancestor in common but descended from a different line.

1. Property acceptable as security for a loan or other obligation.
2. A collateral relative.

[Middle English, from Medieval Latin collaterālis : Latin com-, com- + Latin latus, later-, side.]

The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2009. Published by Houghton Mifflin Company. All rights reserved.