self-defense

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun Defense of oneself when physically attacked.
• noun Defense of what belongs to oneself, as one's works or reputation.
• noun Law The use of force against another person as permitted by the law when that person is perceived as presenting an immediate or imminent threat to one's own life or safety.

from The Century Dictionary.

• noun The act of defending one's own person, property, or reputation; in law, the act of forcibly resisting a forcible attack upon one's own person or property, or upon the persons or property of those whom, by law, one has a right to protect and defend.

from the GNU version of the Collaborative International Dictionary of English.

• noun The act of defending one's own person, property, or reputation.
• noun (Law) in protection of self, -- it being permitted in law to a party on whom a grave wrong is attempted to resist the wrong, even at the peril of the life of the assailiant.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun The means of defending oneself from physical attack.
• noun law The right to protect oneself against violence by using reasonable force, especially when used as justification in a murder charge.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun the act of defending yourself