ballast

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun Heavy material that is placed in the hold of a ship or the gondola of a balloon to enhance stability.
• noun Coarse gravel or crushed rock laid to form a bed for roads or railroads.
• noun The gravel ingredient of concrete.
• noun Something that gives stability, especially in character.
• transitive verb To stabilize or provide with ballast.
• transitive verb To fill (a railroad bed) with or as if with ballast.

from The Century Dictionary.

• Ballasted.
• To place ballast in or on; furnish with ballast: as, to ballast a ship; to ballast a balloon; to ballast the bed of a railroad. See the noun.
• Figuratively: To give steadiness to; keep steady.
• To serve as a counterpoise to; keep down by counteraction.
• To load; freight.
• To load or weigh down.
• noun Weight carried by a ship or boat for the purpose of insuring the proper stability, both to avoid risk of capsizing and to secure the greatest effectiveness of the propelling power.
• noun Bags of sand placed in the car of a balloon to steady it and to enable the aëronaut to lighten the balloon, when necessary to effect a rise, by throwing part of the sand out.
• noun Gravel, broken stones, slag, or similar material (usually called road-metal), placed between the sleepers or ties of a railroad, to prevent them from shifting, and generally to give solidity to the road.
• noun Figuratively, that which gives stability or steadiness, mental, moral, or political.
• noun The rough masonry of the interior of a wall, or that laid upon the vault; masonry used where weight and solidity are needed. Compare filling, 7, and back-filling.

from the GNU version of the Collaborative International Dictionary of English.

• noun (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.
• noun Any heavy matter put into the car of a balloon to give it steadiness.
• noun Gravel, broken stone, etc., laid in the bed of a railroad to make it firm and solid.
• noun The larger solids, as broken stone or gravel, used in making concrete.
• noun Fig.: That which gives, or helps to maintain, uprightness, steadiness, and security.
• noun a steam engine used in excavating and for digging and raising stones and gravel for ballast.
• noun a ship carrying only ballast.
• transitive verb To steady, as a vessel, by putting heavy substances in the hold.
• transitive verb To fill in, as the bed of a railroad, with gravel, stone, etc., in order to make it firm and solid.
• transitive verb To keep steady; to steady, morally.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun nautical Heavy material that is placed in the hold of a ship (or in the gondola of a balloon), to provide stability.
• noun figuratively Anything that steadies emotion or the mind.
• noun Coarse gravel or similar material laid to form a bed for roads or railroads.
• noun construction A material, such as aggregate or precast concrete pavers, which employs its mass and the force of gravity to hold single-ply roof membranes in place.
• noun countable, electronics device used for stabilizing current in an electric circuit (e.g.in a tube lamp supply circuit)
• verb To stabilize or load a ship with ballast.
• verb To lay ballast on the bed of a railroad track.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun any heavy material used to stabilize a ship or airship
• noun an attribute that tends to give stability in character and morals; something that steadies the mind or feelings
• noun a resistor inserted into a circuit to compensate for changes (as those arising from temperature fluctuations)
• noun an electrical device for starting and regulating fluorescent and discharge lamps
• verb make steady with a ballast
• noun coarse gravel laid to form a bed for streets and railroads