Definition of Stimulant:
Stimulants are medicines capaable of exciting the vital energy, whether as exerted in sensation or motion [Brown1878; Meyer1932].
Something that increases activity of functional tissues. Often refers to substances that increase activity of the central nervous system without regard for the inherent capacity of the system to support that activity (i.e. intrinsically exhausting.) May be used to reassert vitality and activity in consort with nervous restoratives (as backup) for restricted periods or to arouse latent potential for activity as a positive agent towards restoring health [Sanchez BOTM680].
Moves things along [Palmer2004].