The Collaborative International Dictionary of English v.0.48:

Mausoleum \Mau`so*le"um\, n.; pl. E. Mausoleums, L. -lea.
   [L. mausoleum, Gr. ?, fr. ? Mausolus, king of Caria, to whom
   Artemisia, his widow, erected a stately monument, one of the
   wonders of the ancient world.]
   A magnificent tomb, or stately sepulchral monument.
   [1913 Webster]

WordNet (r) 3.0 (2006):

mausoleum
    n 1: a large burial chamber, usually above ground

Moby Thesaurus II by Grady Ward, 1.0:

85 Moby Thesaurus words for "mausoleum":
   arch, barrow, beehive tomb, bone house, boundary stone, box grave,
   brass, burial, burial chamber, burial mound, bust, cairn,
   catacombs, cenotaph, charnel house, cist, cist grave, column,
   cromlech, cross, crypt, cup, cyclolith, deep six, dokhma, dolmen,
   footstone, grave, gravestone, headstone, hoarstone, house of death,
   inscription, last home, long home, low green tent, low house,
   marker, mastaba, megalith, memento, memorial, memorial arch,
   memorial column, memorial statue, memorial stone, menhir, monolith,
   monstrance, monument, mound, mummy chamber, narrow house,
   necrology, obelisk, obituary, ossuarium, ossuary, passage grave,
   pillar, pit, plaque, prize, pyramid, reliquary, remembrance,
   resting place, ribbon, rostral column, sepulcher, shaft,
   shaft grave, shrine, stela, stone, stupa, tablet, testimonial,
   tomb, tombstone, tope, tower of silence, trophy, tumulus, vault



The Devil's Dictionary (1881-1906):

MAUSOLEUM, n.  The final and funniest folly of the rich.