AIM-9
An air-to-air missile with a nonnuclear warhead and an infrared, heat-seeking homing device. It was introduced in the 1950s and is still in use today. The ground-to-air equivalent is the Chaparral.
The Sidewinder got its name from early prototypes that zigzagged in flight, owing to off-center placement of the homing device that caused the target to appear to be moving as the missile spun in flight, thus influencing its flight path.
See the Introduction, Abbreviations and Pronunciation for further details.