The Collaborative International Dictionary of English v.0.48:

Durance \Dur"ance\, n. [OF. durance duration, fr. L. durans,
   -antis, p. pr. durare to endure, last. See Dure, and cf.
   Durant.]
   1. Continuance; duration. See Endurance. [Archaic]
      [1913 Webster]

            Of how short durance was this new-made state!
                                                  --Dryden.
      [1913 Webster]

   2. Imprisonment; restraint of the person; custody by a
      jailer; duress. Shak. "Durance vile." --Burns.
      [1913 Webster]

            In durance, exile, Bedlam or the mint. --Pope.
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   3.
      (a) A stout cloth stuff, formerly made in imitation of
          buff leather and used for garments; a sort of tammy or
          everlasting.
          [1913 Webster]

                Where didst thou buy this buff? let me not live
                but I will give thee a good suit of durance.
                                                  --J. Webster.
      (b) In modern manufacture, a worsted of one color used for
          window blinds and similar purposes.
          [1913 Webster]

WordNet (r) 3.0 (2006):

durance
    n 1: imprisonment (especially for a long time)