motivation, motive, need - the psychological feature that arouses an organism to action toward a desired goal; the reason for the action; that which gives purpose and direction to behavior; "we did not understand his motivation"; "he acted with the best of motives"

irrational impulse - a strong spontaneous and irrational motivation; "his first impulse was to denounce them"; "the urge to find out got him into trouble"

cacoethes, mania, passion - an irrational but irresistible motive for a belief or action

obsession, compulsion - an irrational motive for performing trivial or repetitive actions against your will