im·pulse / ˈimˌpəls/ • n. 1. a sudden strong and unreflective urge or desire to act: I had an almost irresistible impulse to giggle | [as adj.] impulse buying. ∎  the tendency to act in this way: he was a man of impulse, not premeditation.2. a driving or motivating force; an impetus: an added impulse to this process of renewal.3. a pulse of electrical energy; a brief current: nerve impulses | a spiral is used to convert radio waves into electrical impulses.4. Physics a force acting briefly on a body and producing a finite change of momentum. ∎  a change of momentum so produced, equivalent to the average value of the force multiplied by the time during which it acts.PHRASES: on impulse (or on an impulse) suddenly and without forethought; impulsively.

impulse (nerve impulse) The signal that travels along the length of a nerve fibre and is the means by which information is transmitted through the nervous system. It is marked by the flow of ions across the membrane of the axon caused by changes in the permeability of the membrane, producing a reduction in potential difference that can be detected as the action potential. The strength of the impulse produced in any nerve fibre is constant (see all-or-none response).

impulse act of impelling; stimulation of the mind. XVII. — L. impulsus, f. pp. stem of impellere IMPEL; cf. PULSE1.
So impulsive impelling to action XVI; actuated by impulse XIX. — (O)F. impulsif, -ive or late L. impulsīvus.

impulse (im-puls) n. (in neurology) see nerve impulse.