The Collaborative International Dictionary of English v.0.48:

Scupper \Scup"per\, n. [OF. escopir, escupir, to spit, perhaps
   for escospir, L. ex + conspuere to spit upon; pref. con- +
   spuere to spit. Cf. Spit, v.] (Naut.)
   An opening cut through the waterway and bulwarks of a ship,
   so that water falling on deck may flow overboard; -- called
   also scupper hole.
   [1913 Webster]

   Scupper hose (Naut.), a pipe of leather, canvas, etc.,
      attached to the mouth of the scuppers, on the outside of a
      vessel, to prevent the water from entering. --Totten.

   Scupper nail (Naut.), a nail with a very broad head, for
      securing the edge of the hose to the scupper.

   Scupper plug (Naut.), a plug to stop a scupper. --Totten.
      [1913 Webster]

WordNet (r) 3.0 (2006):

scupper
    n 1: drain that allows water on the deck of a vessel to flow
         overboard
    v 1: wait in hiding to attack [syn: ambush, scupper,
         bushwhack, waylay, lurk, ambuscade, lie in wait]
    2: put in a dangerous, disadvantageous, or difficult position
       [syn: queer, expose, scupper, endanger, peril]