Bal·last n.
 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 carrying only ballast.