third letter of the Greek alphabet, c. 1400, from Greek gamma, from Phoenician gimel, said to mean literally "camel" (see camel) and to be so called for a fancied resemblance of its shape to some part of a camel. Gamma rays (1903) originally were thought to be a third type of radiation, but later were found to be very short X-rays.

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Definitions of gamma from WordNet
gamma (n.)
the 3rd letter of the Greek alphabet;
gamma (n.)
a unit of magnetic field strength equal to one-hundred-thousandth of an oersted;
Gamma (n.)
Portuguese navigator who led an expedition around the Cape of Good Hope in 1497; he sighted and named Natal on Christmas Day before crossing the Indian Ocean (1469-1524);
Synonyms: da Gamma / Vasco da Gamma