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]