Merriam-Webster's Collegiate® Dictionary, 11th Edition
THROTTLE
I. verb (throttled; throttling)
Etymology: Middle English throtelen, from throte throat
Date: 15th century
transitive verb
1. a. to compress the throat of ; choke , to kill by such action, to prevent or check expression or activity of ; suppress ,
2. to decrease the flow of (as steam or fuel to an engine) by a valve, to regulate and especially to reduce the speed of (as an engine) by such means, to vary the thrust of (a rocket engine) during flight, intransitive verb to throttle something (as an engine), throttler noun
II. noun
Etymology: perhaps from Middle English *throtel, diminutive of throte throat
Date: circa 1547
1. throat 1a, trachea 1,
2. a valve for regulating the supply of a fluid (as steam) to an engine, the lever controlling this valve, the condition of being throttled