(ał′fə) noun
1. The first letter and vowel in the Greek alphabet (A, α); corresponding to English a. As a numeral it denotes 1.
2. The beginning or first of anything.
—the alpha and omega Both the first and the last; beginning and end; the sum total: used of Christ. Rev. i 8.
—adjective
1. Designating the first in order of importance or discovery: alpha test.
2. Chem. Denoting a carbon atom next to a designated carbon in an organic molecule.
3. Physics Denoting the first of a series of radiations or emissions arranged in order of increasing frequency: alpha rays, alpha particle. [ < Gk. < Hebrew aleph OX]

(al′fə) noun Astron.
The principal or brightest star in a constellation.