The Collaborative International Dictionary of English v.0.48:

Tombstone \Tomb"stone`\ (t[=oo]m"st[=o]n`), n.
   A stone or small stone monument erected over a grave, bearing
   the name of the dead person interred there, to preserve the
   memory of the deceased.
   [1913 Webster]

WordNet (r) 3.0 (2006):

tombstone
    n 1: a stone that is used to mark a grave [syn: gravestone,
         headstone, tombstone]

Moby Thesaurus II by Grady Ward, 1.0:

54 Moby Thesaurus words for "tombstone":
   arch, barrow, boundary stone, brass, bust, cairn, cenotaph, column,
   cromlech, cross, cup, cyclolith, dolmen, footstone, grave,
   gravestone, headstone, hoarstone, inscription, ledger, marker,
   mausoleum, megalith, memento, memorial, memorial arch,
   memorial column, memorial statue, memorial stone, menhir, monolith,
   monument, mound, necrology, obelisk, obituary, pillar, plaque,
   prize, pyramid, reliquary, remembrance, ribbon, rostral column,
   shaft, shrine, stela, stone, stupa, tablet, testimonial, tomb,
   tope, trophy



U.S. Gazetteer Places (2000):

Tombstone, AZ -- U.S. city in Arizona
   Population (2000):    1504
   Housing Units (2000): 839
   Land area (2000):     4.299826 sq. miles (11.136498 sq. km)
   Water area (2000):    0.000000 sq. miles (0.000000 sq. km)
   Total area (2000):    4.299826 sq. miles (11.136498 sq. km)
   FIPS code:            74400
   Located within:       Arizona (AZ), FIPS 04
   Location:             31.715940 N, 110.064827 W
   ZIP Codes (1990):     85638
   Note: some ZIP codes may be omitted esp. for suburbs.
   Headwords:
    Tombstone, AZ
    Tombstone