ballast

(bălˈəst)

1. Heavy material that is placed in the hold of a ship or the gondola of a balloon to enhance stability.
2. a. Coarse gravel or crushed rock laid to form a bed for roads or railroads.
   b. The gravel ingredient of concrete.
3. Something that gives stability, especially in character.

1. To stabilize or provide with ballast.
2. To fill (a railroad bed) with or as if with ballast.