The Collaborative International Dictionary of English v.0.48:

docker \docker\ n.
   a laborer who loads and unloads vessels in a port.

   Syn: stevedore, loader, longshoreman, dockhand, dock worker,
        dock-walloper, lumper.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

docker
    n 1: a laborer who loads and unloads vessels in a port [syn:
         stevedore, loader, longshoreman, docker,
         dockhand, dock worker, dockworker, dock-walloper,
         lumper]