Xenon:	A colorless, odorless gas used in electric luminescent tubes to provide a bright light; a xenon stroboscope for ignition timing is strong enough to use in daylight
X tire:	Michelin "X" Radial tires.
x-type engine:	An engine in which the cylinders occur in four rows set at an angle from each other with the crankshaft running through the intersection of the X. The single crankshaft is turned by all banks of cylinders.
x-valve:	There are two kinds of valves in a car, intake and exhaust. The intake valves allow oxygen and fuel into the cylinder head and the exhaust valves allow the used-up gases to exit.