Merriam-Webster's Collegiate® Dictionary, 11th Edition
BETA
I. noun
Etymology: Middle English betha, from Latin beta, from Greek bēta, of Semitic origin; akin to Hebrew bēth beth
Date: 14th century
the 2d letter of the Greek alphabet, beta particle , a measure of the risk potential of a stock or an investment portfolio expressed as a ratio of the stock's or portfolio's volatility to the volatility of the market as a whole, a nearly complete prototype of a product (as software) ,
II. adjective
Date: 1862
second in position in the structure of an organic molecule from a particular group or atom