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The Collaborative International Dictionary of English v.0.48 (gcide)

Beta \Be"ta\, n. [Gr. bh^ta.]
The second letter of the Greek alphabet, B, [beta]. See {B},
and cf. etymology of {Alphabet}.

Note: Beta (B, [beta]) is used variously for classifying, as:
(a) (Astron.) To designate some bright star, usually the
second brightest, of a constellation, as, [beta]
Aurig[ae].
(b) (Chem.) To distinguish one of two or more isomers; also,
to indicate the position of substituting atoms or groups
in certain compounds; as, [beta]-naphthol. With acids, it
commonly indicates that the substituent is in union with
the carbon atom next to that to which the carboxyl group
is attached.
[Webster 1913 Suppl.] Betacism