alpha
1. al.pha \'al-f*\ n [ME, fr. L, fr. Gk, of Sem origin; akin to Heb a-leph aleph] 1: the first letter of the Greek alphabet - symbol A or a 2: something that is first : BEGINNING 3: the chief or brightest star of a constellation 2. alpha or a- aj : closest in the structure of an organic molecule to a particular group or atom {a-substitution} {a-naphthol}