The Collaborative International Dictionary of English v.0.48:

Underbear \Un`der*bear"\, v. t. [AS. underberan. See Under,
   and Bear to support.]
   1. To support; to endure. [Obs.] --Shak.
      [1913 Webster]

   2. To line; to guard; to face; as, cloth of gold underborne
      with blue tinsel. [Obs.] --Shak.
      [1913 Webster]