The Collaborative International Dictionary of English v.0.48:

Collier \Col"lier\, n. [OE. colier. See Coal.]
   1. One engaged in the business of digging mineral coal or
      making charcoal, or in transporting or dealing in coal.
      [1913 Webster]

   2. A vessel employed in the coal trade.
      [1913 Webster]

WordNet (r) 3.0 (2006):

collier
    n 1: someone who works in a coal mine [syn: coal miner,
         collier, pitman]