The Collaborative International Dictionary of English v.0.48:

Spinster \Spin"ster\, n. [Spin + -ster.]
   1. A woman who spins, or whose occupation is to spin.
      [1913 Webster]

            She spake to spinster to spin it out. --Piers
                                                  Plowman.
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            The spinsters and the knitters in the sun. --Shak.
      [1913 Webster]

   2. A man who spins. [Obs.] --Shak.
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   3. (Law) An unmarried or single woman; -- used in legal
      proceedings as a title, or addition to the surname.
      [1913 Webster]

            If a gentlewoman be termed a spinster, she may abate
            the writ.                             --Coke.
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   4. A woman of evil life and character; -- so called from
      being forced to spin in a house of correction. [Obs.]
      [1913 Webster]

WordNet (r) 3.0 (2006):

spinster
    n 1: an elderly unmarried woman [syn: spinster, old maid]
    2: someone who spins (who twists fibers into threads) [syn:
       spinner, spinster, thread maker]

Moby Thesaurus II by Grady Ward, 1.0:

23 Moby Thesaurus words for "spinster":
   bachelor girl, feme sole, jenny, lone woman, maid, maiden,
   maiden lady, mule, old maid, silkworm, single girl, spider,
   spinner, spinning frame, spinning jenny, spinstress, tabby,
   throstle, vestal, vestal virgin, virgin, ,



Bouvier's Law Dictionary, Revised 6th Ed (1856):

SPINSTER. An addition given, in legal writings, to a woman who never was
married. Lovel. on Wills, 269.