Source : Webster's Revised Unabridged Dictionary (1913)

Surcoat \Sur"coat`\, n. [OE. surcote, OF. surcote. See {Sur-},
   and {Coat}, and cf. {Overcoat}.]
   1. A coat worn over the other garments; especially, the long
      and flowing garment of knights, worn over the armor, and
      frequently emblazoned with the arms of the wearer.

            A long surcoat of pers upon he had..  --Chaucer.

            At night, or in the rain, He dons a surcoat which he
            doffs at morn.                        --Emerson.

   2. A name given to the outer garment of either sex at
      different epochs of the Middle Ages.

Source : WordNet®

surcoat
     n 1: a loose outer coat usually of rich material
     2: a tunic worn over a knight's armor