accelerator
     n 1: a pedal that controls the throttle valve; "he stepped on the
          gas" [syn: {accelerator pedal}, {gas pedal}, {gas}, {throttle},
           {gun}]
     2: a valve that regulates the supply of fuel to the engine
        [syn: {throttle}, {throttle valve}]
     3: (chemistry) a substance that initiates or accelerates a
        chemical reaction without itself being affected [syn: {catalyst}]
        [ant: {anticatalyst}]
     4: a scientific instrument that increases the kinetic energy of
        charged particles [syn: {particle accelerator}, {atom
        smasher}]
Source: WordNet® 2.0