The Collaborative International Dictionary of English v.0.48:

Sarcophagus \Sar*coph"a*gus\, n.; pl. L. Sarcophagi, E.
   Sarcophaguses. [L., fr. Gr. sarkofa`gos, properly, eating
   flesh; sa`rx, sa`rkos, flesh + fagei^n to eat. Cf.
   Sarcasm.]
   1. A species of limestone used among the Greeks for making
      coffins, which was so called because it consumed within a
      few weeks the flesh of bodies deposited in it. It is
      otherwise called lapis Assius, or Assian stone, and is
      said to have been found at Assos, a city of Lycia.
      --Holland.
      [1913 Webster]

   2. A coffin or chest-shaped tomb of the kind of stone
      described above; hence, any stone coffin.
      [1913 Webster]

   3. A stone shaped like a sarcophagus and placed by a grave as
      a memorial.
      [1913 Webster]

WordNet (r) 3.0 (2006):

sarcophagus
    n 1: a stone coffin (usually bearing sculpture or inscriptions)

The Devil's Dictionary (1881-1906):

SARCOPHAGUS, n.  Among the Greeks a coffin which being made of a
certain kind of carnivorous stone, had the peculiar property of
devouring the body placed in it.  The sarcophagus known to modern
obsequiographers is commonly a product of the carpenter's art.