The Collaborative International Dictionary of English v.0.48:

Trainman \Train"man`\
   a member of the crew of a railroad train, often an assistant
   to a conductor.
   [PJC]

WordNet (r) 3.0 (2006):

trainman
    n 1: an employee of a railroad [syn: trainman, railroader,
         railroad man, railwayman, railway man]