The Collaborative International Dictionary of English v.0.48:

Smokestack \Smoke"stack`\, n.
   A chimney; esp., a pipe serving as a chimney, as the pipe
   which carries off the smoke of a locomotive, the funnel of a
   steam vessel, etc.
   [1913 Webster]

WordNet (r) 3.0 (2006):

smokestack
    n 1: a large tall chimney through which combustion gases and
         smoke can be evacuated [syn: smokestack, stack]