Source : Webster's Revised Unabridged Dictionary (1913)

Bullion \Bul"lion\ (b[.u]l"y[u^]n), n. [Cf. OE. bullyon a hook
   used for fastening the dress, a button, stud, an embossed
   ornament of various kinds, e. g., on the cover of a book, on
   bridles or poitrels, for purses, for breeches and doublets,
   LL. bullio the swelling of boiling water, a mass of gold or
   silver, fr. L. bulla boss, stud, bubble (see {Bull} an
   edict), or perh. corrupted fr. F. billon base coin, LL.
   billio bullion. Cf. {Billon}, {Billet} a stick.]
   1. Uncoined gold or silver in the mass.

   Note: Properly, the precious metals are called bullion, when
         smelted and not perfectly refined, or when refined, but
         in bars, ingots or in any form uncoined, as in plate.
         The word is often often used to denote gold and silver,
         both coined and uncoined, when reckoned by weight and
         in mass, including especially foreign, or uncurrent,
         coin.

   2. Base or uncurrent coin. [Obs.]

            And those which eld's strict doom did disallow, And
            damm for bullion, go for current now. --Sylvester.

   3. Showy metallic ornament, as of gold, silver, or copper, on
      bridles, saddles, etc. [Obs.]

            The clasps and bullions were worth a thousand pound.
                                                  --Skelton.

   4. Heavy twisted fringe, made of fine gold or silver wire and
      used for epaulets; also, any heavy twisted fringe whose
      cords are prominent.

Source : WordNet®

bullion
     n 1: a mass of precious metal
     2: gold or silver in bars or ingots