1. Something causing or regarded as causing a response.
2. An agent, action, or condition that elicits or accelerates a physiological or psychological activity or response.
3. Something that incites or rouses to action; an incentive: "Works which were in themselves poor have often proved a stimulus to the imagination" (W.H. Auden).

[Latin, goad.]

The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2009. Published by Houghton Mifflin Company. All rights reserved.