de·fen·sive 
(dĭ-fĕnsĭv)
(dĭ-fĕnsĭv)adj.
1. Intended or appropriate for defending; protective.
2.
a. Intended to withstand or deter aggression or attack: a defensive weapons system; defensive behavior.
b. Of or relating to the effort to prevent an opponent from gaining points in a game or athletic contest.
c. Performed so as to avoid risk, danger, or legal liability: defensive driving; defensive medicine.
3. Of or relating to defense.
4. Psychology Constantly protecting oneself from criticism, exposure of one's shortcomings, or other real or perceived threats to the ego.
n.
Idiom: 1. A means of defense.
2. An attitude or position of defense.
on the defensive
Prepared to withstand or counter aggression or attack.
de·fensive·ly adv.
de·fensive·ness n.