The Collaborative International Dictionary of English v.0.48:

Lighter \Light"er\, n. [D. ligter, fr. ligt light. See Light
   not heavy.] (Naut.)
   A large boat or barge, mainly used in unloading or loading
   vessels which can not reach the wharves at the place of
   shipment or delivery.
   [1913 Webster]

   Lighter screw (Mach.), a screw for adjusting the distance
      between the stones in a grinding mill by raising or
      lowering the bridgetree.
      [1913 Webster]