WordNet sense 1 ((chemistry) a substance that initiates or accelerates a chemical reaction without itself being affected):

catalyst

WordNet sense 2 (a pedal that controls the throttle valve):

gas, gun, throttle, accelerator pedal, gas pedal

WordNet sense 3 (a scientific instrument that increases the kinetic energy of charged particles):

atom smasher, particle accelerator

WordNet sense 4 (a valve that regulates the supply of fuel to the engine):

throttle valve