I. ˈga-mə noun
Etymology: Middle English, from Late Latin, from Greek, of Semitic origin; akin to Hebrew gīmel gimel
Date: 15th century
1. : the 3d letter of the Greek alphabet — see alphabet table
2. : the degree of contrast of a developed photographic image or of a video image
3. : a unit of magnetic flux density equal to one nanotesla
4. : gamma ray
gamma counter
5. : microgram
II. adjective
Date: 1896
1. : of, relating to, or being one of three or more closely related chemical substances
2. : third in position in the structure of an organic molecule from a particular group or atom — symbol γ