Word Study
bas-relief
CIDE DICTIONARY
bas-relief, 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]
OXFORD DICTIONARY
bas-relief, n. sculpture or carving in which the figures project slightly from the background.
Etymology
earlier basse relieve f. It. basso rilievo low relief: later altered to F form
For further exploring for "bas-relief" in Webster Dictionary Online