[be.ta] n [ME betha, fr. L beta, fr. Gk beta, of Sem origin; akin to Heb beth beth] (14c) 1: the 2d letter of the Greek alphabet
2: beta particle
3: a measure of a stock's or a portfolio's volatility that is expressed numerically as deviation from the market's volatility taken as unity
[2]beta adj (1899): second in position in the structure of an organic molecule from a particular group or atom "~ substitution"--often used in combination