The Collaborative International Dictionary of English v.0.48:

Unload \Un*load"\, v. t. [1st pref. un- + load.]
   1. To take the load from; to discharge of a load or cargo; to
      disburden; as, to unload a ship; to unload a beast.
      [1913 Webster]

   2. Hence, to relieve from anything onerous.
      [1913 Webster]

   3. To discharge or remove, as a load or a burden; as, to
      unload the cargo of a vessel.
      [1913 Webster]

   4. To draw the charge from; as, to unload a gun.
      [1913 Webster]

   5. To sell in large quantities, as stock; to get rid of.
      [Brokers' Cant, U. S.]
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Unload \Un*load"\, v. i.
   To perform the act of unloading anything; as, let unload now.
   [1913 Webster]

WordNet (r) 3.0 (2006):

unload
    v 1: leave or unload; "unload the cargo"; "drop off the
         passengers at the hotel" [syn: drop, drop off, set
         down, put down, unload, discharge]
    2: take the load off (a container or vehicle); "unload the
       truck"; "offload the van" [syn: unload, unlade,
       offload]

Moby Thesaurus II by Grady Ward, 1.0:

62 Moby Thesaurus words for "unload":
   alleviate, be light, break bulk, clear the trade, close out,
   convert, convert into cash, cut under, debark, disburden,
   discharge, disembark, disembarrass, disencumber, dump, ease,
   effect a sale, empty, have little weight, jettison, job,
   kick the beam, land, lighten, liquidate, make a sale, make light,
   make lighter, market, merchandise, move, off-load, offload,
   reduce weight, relieve, resell, retail, sacrifice, sell, sell off,
   sell on consignment, sell out, sell over, sell retail, sell short,
   sell up, sell wholesale, set at ease, stevedore,
   terminate the account, turn into money, turn over, unballast,
   unburden, undercut, undersell, unfreight, unlade, unpack, unship,
   weigh lightly, wholesale