Longman Dictionary of Contemporary English - impulse

~ n 1 a sudden strong desire to do something before thinking whether it is a sensible thing to do  (impulse to do sth)  (Gerry couldn't resist the impulse to skip work and go down to the beach. | on impulse (=because of an impulse))  (She had invited Joseph on a sudden impulse but was now regretting it. | impulse buying (=buying things without planning or choosing carefully)) 2 an aim or reason that causes a particular kind of activity or behaviour  (The prime impulse of capitalism is the making of money.) 3 technical a single push or force moving for a short time in one direction along a nerve or electric wire