The Collaborative International Dictionary of English v.0.48:

Mogul \Mo*gul"\, n. [From the Mongolian.]
   1. A person of the Mongolian race.
      [1913 Webster]

   2. Specifically: Any of the Mongolian peoples who conquered
      parts of India and established an empire lasting from 1526
      to 1857. Also, any of their descendents.
      [PJC]

   3. (Railroad) A heavy locomotive for freight traffic, having
      three pairs of connected driving wheels and a two-wheeled
      truck.
      [1913 Webster]

   4. A great personage; magnate; autocrat; as, an industrial
      mogul.
      [Webster 1913 Suppl.]

   Great Mogul, or Grand Mogul, the sovereign of the empire
      founded in Hindustan by the Mongols under Baber in the
      sixteenth century. Hence, a very important personage; a
      lord; -- sometimes only mogul or Moghul. --Dryden.
      [1913 Webster] Moghul

The Collaborative International Dictionary of English v.0.48:

Moghul \Mo*ghul"\, Mogul \Mo*gul"\, prop. a. [See Mogul, n..]
   Of or pertaining to the Moguls[2]; as, The Taj Mahal, the
   most beautiful piece of Mogul architecture, was built by the
   Mogul emperor Shah Jehan as a mausoleum for his favorite
   wife.
   [PJC] Moghul empire

WordNet (r) 3.0 (2006):

mogul
    n 1: a bump on a ski slope
    2: a member of the Muslim dynasty that ruled India until 1857
       [syn: Mogul, Moghul]
    3: a very wealthy or powerful businessman; "an oil baron" [syn:
       baron, big businessman, business leader, king,
       magnate, mogul, power, top executive, tycoon]