WordNet (r) 3.0 (2006):

bas relief
    n 1: a sculptural relief in which forms extend only slightly
         from the background; no figures are undercut [syn: bas
         relief, low relief, basso relievo, basso rilievo]
         [ant: alto relievo, alto rilievo, high relief]

Moby Thesaurus II by Grady Ward, 1.0:

39 Moby Thesaurus words for "bas relief":
   anaglyph, bellying, boldness, boss, bulging, cameo, cameo glass,
   cavo-rilievo, cut glass, embossment, eminence, excrescence,
   excrescency, extrusion, gibbosity, gibbousness, glyph, glyptograph,
   high relief, intaglio, intaglio rilevato, intaglio rilievo,
   low relief, mask, medal, medallion, plaquette, projection,
   prominence, protrusion, protuberance, protuberancy, relief,
   relievo, salience, salient, sculptured glass, tuberosity,
   tuberousness