WordNet (r) 3.0 (2006):

unloading
    n 1: the labor of taking a load of something off of or out of a
         vehicle or ship or container etc. [ant: loading]

Moby Thesaurus II by Grady Ward, 1.0:

36 Moby Thesaurus words for "unloading":
   alleviation, cleaning out, clearance, clearing, defecation,
   depletion, disburdening, discharging cargo, disembarrassment,
   disencumberment, disencumbrance, drainage, draining, easement,
   easing, egress, elimination, emptying, evacuation, excretion,
   exhausting, exhaustion, lightening, off-loading, relief, removal,
   unballasting, unburdening, unfreighting, unlading, unsaddling,
   untaxing, unweighting, venting, voidance, voiding