defensive

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

• adjective Intended or appropriate for defending; protective.
• adjective Intended to withstand or deter aggression or attack.
• adjective Of or relating to the effort to prevent an opponent from gaining points in a game or athletic contest.
• adjective Performed so as to avoid risk, danger, or legal liability.
• adjective Of or relating to defense.
• adjective Psychology Constantly protecting oneself from criticism, exposure of one's shortcomings, or other real or perceived threats to the ego.
• noun A means of defense.
• noun An attitude or position of defense.
• idiom (on the defensive) Prepared to withstand or counter aggression or attack.

from The Century Dictionary.

• Serving to defend; proper for defense: as, defensive armor.
• Of the nature of defense; consisting in resisting attack or aggression: as, defensive war, in distinction from offensive war, which is aggressive.
• In a state or posture to defend: as, a defensive attitude.
• noun That which defends or serves for defense; a safeguard; a security.

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

• adjective Serving to defend or protect; proper for defense; opposed to offensive.
• adjective Carried on by resisting attack or aggression; -- opposed to offensive.
• adjective In a state or posture of defense.
• noun That which defends; a safeguard.
• noun to be or stand in a state or posture of defense or resistance, in opposition to aggression or attack.

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

• adjective Intended for defence; protective
• adjective Intended to deter attack
• adjective Performed so as to minimise risk
• adjective Displaying an inordinate sensitivity to criticism; compare paranoid
• adjective cricket Of a bowling or fielding tactic designed to prevent the other side from scoring runs.; of a batting tactic designed to prevent being out.
• adjective sports pertaining to defense, as opposed to attack.
• noun A means, attitude or position of defense.

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

• adjective intended or appropriate for defending against or deterring aggression or attack
• adjective attempting to justify or defend in speech or writing
• noun an attitude of defensiveness (especially in the phrase `on the defensive')