The Collaborative International Dictionary of English v.0.48:

Bas-relief \Bas`-re*lief"\, n. [F. bas-relief; bas low + relief
   raised work, relever to raise: cf. It. bassorilievo.]
   Low relief; sculpture, the figures of which project less than
   half of their true proportions; -- called also bass-relief
   and basso-rilievo. See Alto-rilievo.
   [1913 Webster]