The Collaborative International Dictionary of English v.0.48:

Coalpit \Coal"pit`\, n.
   1. A pit where coal is dug.
      [1913 Webster]

   2. A place where charcoal is made. [U. S.]
      [1913 Webster]

WordNet (r) 3.0 (2006):

coalpit
    n 1: a mine where coal is dug from the ground [syn: coal mine,
         coalpit]