Meaning of GAMMA in English

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

Merriam Webster. Explanatory English dictionary Merriam Webster.      Толковый словарь английского языка Мерриам-Уэбстер.