The Collaborative International Dictionary of English v.0.48:

Gum \Gum\, v. t. [imp. & p. p. Gummed (g[u^]md); p. pr. & vb.
   n. Gumming.]
   1. To smear with gum; to close with gum; to unite or stiffen
      by gum or a gumlike substance; to make sticky with a
      gumlike substance.
      [1913 Webster]

            He frets like a gummed velvet.        --Shak.
      [1913 Webster]

   2. To chew with the gums, rather than with the teeth.
      [PJC]

   gum up
      (a) To block or clog (a conduit) with or as if with gum;
          as, to gum up the drainpipe.
      (b) to interfere with; to spoil. [Slang]
          [PJC]

WordNet (r) 3.0 (2006):

gum up
    v 1: stick together as if with gum; "the inside of the pipe has
         gummed up"

Moby Thesaurus II by Grady Ward, 1.0:

33 Moby Thesaurus words for "gum up":
   ball up, bitch, bitch up, blow, bobble, bollix, bollix up,
   bonehead into it, bugger, bugger up, bungle, cook, crab, cramp,
   crimp, drop a brick, flub, foul up, goof, goof up, gum, hash up,
   louse up, mess up, muck up, mucker, play hell with, play hob with,
   queer, screw up, sink, snafu, snarl up