alpha

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun The first letter of the Greek alphabet.
• noun The first of a series; the beginning.
• noun Astronomy The brightest star in a constellation.
• noun The mathematical estimate of the return on a security when the return on the market as a whole is zero. Alpha is derived from a in the formula R_i = a + bR_m, which measures the return on a security (R_i) for a given return on the market (R_m) where b is beta.
• noun The return on an investment portfolio that can be attributed to the skill of the portfolio's manager rather than the performance of the market.
• adjective Being the highest ranked or most dominant individual of one's sex. Used of social animals.
• adjective Being in the first position relative to a designated carbon atom in an organic molecule at which an atom or a group may be substituted.
• adjective Referring to the first of a group of isomers, or molecules of similar origin or properties, determined arbitrarily by those who discover or classify them. Used in combination.
• adjective Alphabetical.

from The Century Dictionary.

• noun The first letter in the Greek alphabet (A, α), answering to A.
• noun The first; the beginning: as in the phrase “alpha and omega,” the beginning and the end, the first and the last, omega being the last letter of the Greek alphabet.
• noun As a classifier: In astronomy, the chief star of a constellation. In chem., the first of two or more isomerous modifications of the same organic compound, as alpha-naphthol, in distinction from beta-naphthol.
• noun In natural history, the first subspecies, etc.
• noun [capitalized] The name given by Carl Neumann, the mathematical physicist, to a supposed body to which all motion, especially motion of rotation, is relative.

from the GNU version of the Collaborative International Dictionary of English.

• noun The first letter in the Greek alphabet, answering to A, and hence used to denote the beginning.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun The name of the first letter of the Greek alphabet (Α,  α), followed by beta. In the Latin alphabet it is the predecessor to A.
• noun Latin alpha
• noun sciences The name of the symbols Α and α used in science and mathematics, often interchangeable with the symbols when used as a prefix.
• noun finance The return of a given asset or portfolio adjusted for systematic risk.
• noun An alpha male.
• noun informal, abbreviation Alphabet.
• adjective Designates the first in an order of precedence.
• adjective associated with the alpha male/female archetype.
• adjective astronomy Designates the brightest star in a constellation.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• adjective first in order of importance
• noun the beginning of a series or sequence
• adjective early testing stage of a software or hardware product
• noun the 1st letter of the Greek alphabet