Bal″last (băl″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 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.