Ballast

1. a. Fig.: That which gives, or helps to maintain, uprightness, steadiness, and security.
2. a. 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.
3. a. Any heavy matter put into the car of a balloon to give it steadiness.
4. a. Gravel, broken stone, etc., laid in the bed of a railroad to make it firm and solid.
5. a. The larger solids, as broken stone or gravel, used in making concrete.

The word meanings were obtained from OPTED(The Online Plain Text English Dictionary), which is based on “The Project Gutenberg Etext of Webster’s Unabridged Dictionary” which is in turn based on the 1913 US Webster’s Unabridged Dictionary (See Project Gutenburg), as a text file.