1. the second letter of the Greek alphabet (β, B).
  2. the consonant sound represented by this letter.
  3. (initial capital letter) Astronomy. a star that is usually the second brightest of a constellation: The second brightest star in Taurus is Beta Tauri.
  4. Chemistry.
    1. one of the possible positions of an atom or group in a compound.
    2. one of two or more isomeric compounds.
  5. the second of any series, as in chemistry or physics.
  6. 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.
  7. (initial capital letter) Trademark. a brand of tape format for VCR tape, incompatible with other formats.Compare VHS.
  8. 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).


  1. the second letter in the Greek alphabet (Β, β), a consonant, transliterated as b
  2. the second highest grade or mark, as in an examination
  3. (modifier)
    1. involving or relating to electronsbeta emitter
    2. relating to one of two or more allotropes or crystal structures of a solidbeta iron
    3. relating to one of two or more isomeric forms of a chemical compound


  1. (foll by the genitive case of a specified constellation) a star in a constellation, usually the second brightestBeta Persei

second letter of the Greek alphabet, c.1300, from Greek, from Hebrew/Phoenician beth (see alphabet); used to designate the second of many things. Beta radiation is from 1899 (Rutherford). Beta particle is attested from 1904.


  1. The second letter of the Greek alphabet.
  2. The second item in a series or system of classification.
  3. A beta particle.
  4. A beta ray.


  1. Of or relating to the second position from a designated carbon atom in an organic molecule at which an atom or a radical may be substituted.
  2. Of or relating to an isomeric variation of a chemical compound, such as a stereoisomer.

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