See stimulus in Webster's New World Roget's A-Z Thesaurus II
noun
Something that causes and encourages a given response:
encouragement, fillip, impetus, impulse, incentive, inducement, motivation, prod, push, spur, stimulant, stimulation, stimulator. See causeSomething that incites especially a violent response:
goad, incitation, incitement, instigation, provocation, trigger. See cause
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