- A substance that renders another substance (a catalyst) active, or that accelerates a process or reaction.
- The fragment produced by chemical cleavage of a proactivator, that induces the enzymic activity of another substance.
- An apparatus for making substances radioactive (a neutron generator or a cyclotron).
- A removable type of myofunctional orthodontic appliance that acts as a passive transmitter of force, produced by the function of the activated muscles, to the teeth and alveolar process that are in contact with it.
- A protein that binds to a DNA sequence before RNA polymerase transcription, sometimes referred to as coactivator.