beta

Concise Oxford English Dictionary © 2008 Oxford University Press:
beta /ˈbiːtə/

▶noun

• 1 the second letter of the Greek alphabet (Β, β), transliterated as ‘b’.

  ■ [as modifier] denoting the second of a series of items or categories.

  ■ Brit. a second-class mark given for a piece of work.

• 2 [as modifier] relating to beta decay or beta particles.

• 3 (also beta coefficient) a measure of the movement in price of a security relative to the stock market, used to indicate possible risk.

– origin via L. from Gk.