gamma ray

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. Electromagnetic radiation emitted by radioactive decay and having energies in a range from ten thousand (10⁴) to ten million (10⁷) electron volts.

Wiktionary

1. n. Very high frequency (and therefore very high energy) electromagnetic radiation emitted as a consequence of radioactivity.

GNU Webster's 1913

1. n. (Physics) A very penetrating electromagnetic ray not appreciably deflected by a magnetic or electric field, emitted by radioactive substances. Gamma rays are photons of electromagnetic radiation having a wavelength shorter than that of X-rays, (i. e. shorter than 0.1 nanometer) and are correspondingly more penetrating than X-rays. In addition to being given off in certain types of radioactive decay, they may be found in cosmic radiation, though they are largely absorbed by the earth's atmosphere. Gamma-ray detectors orbited above the atmosphere have found bursts of gamma radiation, in some cases associated with visually observed supernova explosions, but in most cases from unidentified sources.

WordNet 3.0

1. n. electromagnetic radiation emitted during radioactive decay and having an extremely short wavelength