The Collaborative International Dictionary of English v.0.48:

Shale \Shale\, n. [AS. scealy, scalu. See Scalme, and cf.
   Shell.]
   1. A shell or husk; a cod or pod. "The green shales of a
      bean." --Chapman.
      [1913 Webster]

   2. [G. shale.] (Geol.) A fine-grained sedimentary rock of a
      thin, laminated, and often friable, structure.
      [1913 Webster]

   Bituminous shale. See under Bituminous.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Shale \Shale\, v. t.
   To take off the shell or coat of; to shell.
   [1913 Webster]

         Life, in its upper grades, was bursting its shell, or
         was shaling off its husk.                --I. Taylor.
   [1913 Webster]

WordNet (r) 3.0 (2006):

shale
    n 1: a sedimentary rock formed by the deposition of successive
         layers of clay