noun

1. the first letter of the Greek alphabet (Α, α)
2. the beginning of anything
3. Astron. the name assigned to the brightest star in each constellation: followed by the constellation's name in the genitive case, as Alpha Centauri

Etymology: Gr < NW Sem: cf. Heb alef, aleph

adjective

1. designating or of the socially dominant member of a group, esp. of a group of animals the alpha male
2. Chem. designating the first of two or more positions in which the substituting atom or radical appears relative to some particular carbon atom in an organic compound: usually written α-: the other positions, in order, are beta (β-), gamma (γ-), delta (δ-), etc.