The Collaborative International Dictionary of English v.0.48:

Slabby \Slab"by\, a. [Compar. Slabbier; superl. Slabbiest.]
   [See Slab, a.]
   1. Thick; viscous.
      [1913 Webster]

            They present you with a cup, and you must drink of a
            slabby stuff.                         --Selden.
      [1913 Webster]

   2. Sloppy; slimy; miry. See Sloppy. --Gay.
      [1913 Webster]

Moby Thesaurus II by Grady Ward, 1.0:

99 Moby Thesaurus words for "slabby":
   adhesive, amylaceous, barfy, clabbered, clammy, clotted,
   coagulated, crappy, curdled, dirty, disgusting, doughy, fecal,
   feculent, fetid, filthy, flyblown, foul, gaumy, gelatinous, glairy,
   gloppy, gluelike, gluey, glutenous, glutinose, glutinous, gooey,
   grumous, gumbo, gumbolike, gumlike, gummous, gummy, gunky, heavy,
   icky, inspissated, jelled, jellied, jellylike, maggoty, malodorous,
   mephitic, miry, mucilaginous, mucky, muddy, nasty, nauseating,
   odious, oozy, ordurous, pasty, plashy, puky, putrid, rank,
   repulsive, ropy, rotten, scabby, scummy, scurfy, shitty, slimy,
   slithery, slobby, sloppy, sloshy, sloughy, sludgy, slushy, soft,
   splashy, sposhy, squashy, squelchy, squishy, starchy, sticky,
   stodgy, stringy, syrupy, tacky, tenacious, thick, thickened, tough,
   tremelloid, tremellose, turbid, vile, viscid, viscose, viscous,
   vomity, wormy, yecchy