The Collaborative International Dictionary of English v.0.48:

Topgallant \Top`gal"lant\, a.
   [1913 Webster]
   1. (Naut.) Situated above the topmast and below the royal
      mast; designatb, or pertaining to, the third spars in
      order from the deck; as, the topgallant mast, yards,
      braces, and the like. See Illustration of Ship.
      [1913 Webster]

   2. Fig.: Highest; elevated; splendid. "The consciences of
      topgallant sparks." --L'Estrange.
      [1913 Webster]

   Topgallant breeze, a breeze in which the topgallant sails
      may properly be carried.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Topgallant \Top`gal"lant\, n.
   1. (Naut.) A topgallant mast or sail.
      [1913 Webster]

   2. Fig.: Anything elevated or splendid. --Bacon.
      [1913 Webster]

WordNet (r) 3.0 (2006):

topgallant
    n 1: a sail set on a yard of a topgallant mast [syn:
         topgallant, topgallant sail]
    2: a mast fixed to the head of a topmast on a square-rigged
       vessel [syn: topgallant, topgallant mast]