Beta

the second letter of the Greek alphabet (β, B).
the consonant sound represented by this letter.
(initial capital letter) Astronomy. a star that is usually the second brightest of a constellation:
The second brightest star in Taurus is Beta Tauri.
Chemistry.

one of the possible positions of an atom or group in a compound.
one of two or more isomeric compounds.

the second of any series, as in chemistry or physics.
Also called beta coefficient, beta line. Stock Exchange. an arbitrary measure of the volatility of a given stock using an index of the volatility of the market as a whole:
A beta of 1.1 indicates a stock that is 10 percent more volatile than the market.
(initial capital letter) Trademark. a brand of tape format for VCR tape, incompatible with other formats.
Compare VHS.
Chiefly British. a grade showing that a student is in the middle or second of three scholastic sections in a class.
Compare alpha (def 7), gamma (def 9).
Contemporary Examples

The CIA Tried Hard to Recruit Spies Among the Al Qaeda Prisoners at Gitmo Daniel Klaidman November 27, 2013
Fired From a Real-Life Glee Dan Crane October 8, 2010
Twenty Years of Alzheimer’s Research May Have Focused on the Wrong Protein Elizabeth Lopatto April 3, 2014
What Did Facebook Change Now? Brian Ries September 20, 2011
From War to Work: Why and How Companies Should Hire Post-9/11 Veterans Zachary Iscol October 30, 2012

Historical Examples

A Brief Account of Radio-activity Francis Preston Venable
The Forbidden Trail Honor Willsie
Pagan Passions Gordon Randall Garrett
Pagan Passions Gordon Randall Garrett
Oomphel in the Sky Henry Beam Piper

noun
the second letter in the Greek alphabet (Β, β), a consonant, transliterated as b
the second highest grade or mark, as in an examination
(modifier)

involving or relating to electrons: beta emitter
relating to one of two or more allotropes or crystal structures of a solid: beta iron
relating to one of two or more isomeric forms of a chemical compound

noun
(foll by the genitive case of a specified constellation) a star in a constellation, usually the second brightest: Beta Persei
n.

adj.