(n): a lever that is operated with the foot
(n): a valve that regulates the supply of fuel to the engine
(n): control consisting of a mechanical device for controlling the flow of a fluid
(n): (chemistry) a substance that initiates or accelerates a chemical reaction without itself being affected
(n): (biology) any agency bringing about activation; a molecule that increases the activity of an enzyme or a protein that increases the production of a gene product in DNA transcription
(n): a scientific instrument that increases the kinetic energy of charged particles
(n): an instrument used by scientists
