activator

Short definition from Wiktionary

Noun

1. 1
   One who, or that which, activates.
2. 2
   Something that activates a catalyst
3. 3
   Any chemical or agent which regulates one or more genes by increasing the rate of transcription.
4. 4
   A type of effector that increases the rate of enzyme-mediated reactions.
5. 5
   A type of dopant used in phosphors and scintillators.
6. 6
   An agent that enables the flotation of a mineral or minerals.
7. 7
   A hand-held device that delivers a controlled fast thrust to a joint, muscle, etc., to help stimulate nervous system activity.