1. The science that deals with mental processes and behavior.

2. The emotional and behavioral characteristics of an individual, a group, or those engaged in a given activity: the psychology of war.

3. Subtle tactical action or argument used to manipulate or influence another: He used poor psychology on his employer when trying to make the point.

4. Philosophy The branch of metaphysics that studies the soul, the mind, and the relationship of life and mind to the functions of the body.