Source : Webster's Revised Unabridged Dictionary (1913)

Ballast \Bal"last\, n. [D. ballast; akin to Dan. baglast,
   ballast, OSw. barlast, Sw. ballast. The first part is perh.
   the same word as E. bare, adj.; the second is last a burden,
   and hence the meaning a bare, or mere, load. See {Bare}, a.,
   and {Last} load.]
   1. (Naut.) Any heavy substance, as stone, iron, etc., put
      into the hold to sink a vessel in the water to such a
      depth as to prevent capsizing.

   2. Any heavy matter put into the car of a balloon to give it
      steadiness.

   3. Gravel, broken stone, etc., laid in the bed of a railroad
      to make it firm and solid.

   4. The larger solids, as broken stone or gravel, used in
      making concrete.

   5. Fig.: That which gives, or helps to maintain, uprightness,
      steadiness, and security.

            It [piety] is the right ballast of prosperity.
                                                  --Barrow.

   {Ballast engine}, a steam engine used in excavating and for
      digging and raising stones and gravel for ballast.

   {Ship in ballast}, a ship carring only ballast.