The Collaborative International Dictionary of English v.0.48:

Nawab \Na*wab"\, n. [See Nabob.]
   1. A deputy ruler or viceroy in India; also, a title given by
      courtesy to other persons of high rank in the East.
      [1913 Webster]

   2. A rich, retired Anglo-Indian; a nabob.
      [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

nawab
    n 1: a governor in India during the Mogul empire [syn: nawab,
         nabob]