WordNet (r) 3.0 (2006):

polka dot
    n 1: design consisting of a pattern of regularly spaced circular
         spots

Moby Thesaurus II by Grady Ward, 1.0:

103 Moby Thesaurus words for "polka dot":
   bespangled, birthmark, blaze, blemish, blotch, blotched, blotchy,
   brand, caste mark, check, checkmark, cicatrix, cut, dapple,
   dappledness, dappleness, discoloration, dot, dotted, dottedness,
   dotty, earmark, engraving, flea-bitten, fleck, flecked, fleckered,
   flick, frecked, freckle, freckled, freckliness, freckly, gash,
   graving, hack, jot, lentigo, macula, macular, maculate, maculated,
   maculation, macule, mark, marking, mole, mottle, mottledness,
   nevus, nick, notch, patch, patchy, peppered, pocked, pockmarked,
   pocky, point, pointillage, pointille, pointillism, pointillistic,
   prick, punctated, puncture, scar, scarification, score, scotch,
   scratch, scratching, spangled, speck, specked, speckle, speckled,
   speckledy, speckliness, speckly, splash, splotch, splotched,
   splotchy, spot, spotted, spottedness, spottiness, spotty,
   sprinkled, stain, stigma, stipple, stippled, stippledness,
   stippling, strawberry mark, studded, tattoo, tattoo mark, tick,
   tittle, watermark