a. An impelling force; an impetus.
b. The motion produced by such a force.
2. A sudden wish or urge that prompts an unpremeditated act or feeling; an abrupt inclination: had an impulse to run away; an impulse of regret that made me hesitate; bought a hat on impulse.
3. A motivating force or tendency: "Respect for the liberty of others is not a natural impulse in most men" (Bertrand Russell).
4. Electronics A surge of electrical power in one direction.
5. Physics The product obtained by multiplying the average value of a force by the time during which it acts. The impulse equals the change in momentum produced by the force in this time interval.
6. Physiology The electrochemical transmission of a signal along a nerve fiber that produces an excitatory or inhibitory response at a target tissue, such as a muscle or another nerve.
Characterized by impulsiveness or acting on impulse: an impulse shopper; impulse buying.
[Latin impulsus, from past participle of impellere, to impel; see IMPEL.]
The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2019 by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Indo-European & Semitic Roots Appendices
Thousands of entries in the dictionary include etymologies that trace their origins back to reconstructed proto-languages. You can obtain more information about these forms in our online appendices:
The Indo-European appendix covers nearly half of the Indo-European roots that have left their mark on English words. A more complete treatment of Indo-European roots and the English words derived from them is available in our Dictionary of Indo-European Roots.