Source : Webster's Revised Unabridged Dictionary (1913)

Portcullis \Port*cul"lis\, v. t. [imp. & p. p. {Portcullised};
   p. pr. & vb. n. {Portcullising}.]
   To obstruct with, or as with, a portcullis; to shut; to bar.
   [R.] --Shak.

Portcullis \Port*cul"lis\, n. [OF. porte coulisse, cole["i]ce, a
   sliding door, fr. L. colare, colatum, to filter, to strain:
   cf. F. couler to glide. See {Port} a gate, and cf. {Cullis},
   {Colander}.]
   1. (Fort.) A grating of iron or of timbers pointed with iron,
      hung over the gateway of a fortress, to be let down to
      prevent the entrance of an enemy. ``Let the portcullis
      fall.'' --Sir W. Scott.

            She . . . the huge portcullis high updrew. --Milton.

   2. An English coin of the reign of Elizabeth, struck for the
      use of the East India Company; -- so called from its
      bearing the figure of a portcullis on the reverse.

Source : WordNet®

portcullis
     n : gate consisting of an iron or wooden grating that hangs in
         the entry to a castle or fortified town; can be lowered
         to prevent passage