n. 25B6; noun
caffeine is a stimulant : TONIC, restorative; antidepressant; informal pep pill, upper, pick-me-up, bracer; Medicine analeptic.
a stimulant to discussion : STIMULUS, incentive, encouragement, impetus, inducement, fillip, boost, spur, prompt; informal shot in the arm.
sedative, downer, deterrent.