noun
spur, inducement, motivation, motive, stimulus, stimulation, spring, impetus, catalyst, ground, provocation, enticement, temptation, bait, consideration, determinant, excuse, rationale, goad, prod, whip, urge, impulse, influence, lure, come-on*, allurement, persuasion, inspiration, exhortation, encouragement, instigation, incitement, reason why, carrot*; see also impulse 1, purpose 1, reason 3.