1. Defense of oneself when physically attacked: took a course in self-defense.
2. Defense of what belongs to oneself, as one's works or reputation.
3. Law. The right to protect oneself against violence or threatened violence with whatever force or means are reasonably necessary.

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.