The Collaborative International Dictionary of English v.0.48:

Loader \Load"er\, n.
   One who, or that which, loads; a mechanical contrivance for
   loading, as a gun.
   [1913 Webster]

WordNet (r) 3.0 (2006):

loader
    n 1: a laborer who loads and unloads vessels in a port [syn:
         stevedore, loader, longshoreman, docker,
         dockhand, dock worker, dockworker, dock-walloper,
         lumper]
    2: an attendant who loads guns for someone shooting game