n. The third letter of the Greek alphabet, Γ, γ, represented historically by c, phonetically by g, in the Roman and English alphabet.n. In entomology, a common European noctuid moth of the family Plusiidæ, Plusia gamma. Also called silver-Y and gamma-moth, from the shape of a silvery spot on the wing, like that of Greek gamma, γ, or English Y. The larva feeds on various low plants.n. Same as gamut.n. A proposed unit of magnetic intensity, equal to one hundred thousandth of a gilbert per second.