The Collaborative International Dictionary of English v.0.48:

Taj Mahal \Taj Ma*hal"\ (t[aum]j m[.a]*h[aum]l"), prop. n.
   [Corruption of Per. Mumt[=a]z-i-Ma[.h]al, lit., the
   distinguished one of the palace, fr. Ar.]
   A marble mausoleum built at Agra, India, by the Mogul Emperor
   Shah Jahan, in memory of his favorite wife. In beauty of
   design and rich decorative detail it is one of the best
   examples of Saracenic architecture, and specifically of Mogul
   architecture.
   [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

Taj Mahal
    n 1: beautiful mausoleum at Agra built by the Mogul emperor Shah
         Jahan (completed in 1649) in memory of his favorite wife