ballast

UK: /ˈbæləst/ US: /ˈbæləst/ ,(bal′əst)

WordReference Random House Learner's Dictionary of American English © 2026

bal•last /ˈbæləst/   n. [uncountable]

1. Nautical heavy material such as rock carried on ships to make them heavier and more controllable.
2. Rail Transport gravel or broken stone placed under the ties of a railroad to keep the tracks steady.

WordReference Random House Unabridged Dictionary of American English © 2026

bal•last  (bal′əst), n. 

1. Nautical any heavy material carried temporarily or permanently in a vessel to provide desired draft and stability.
2. Aeronautics something heavy, as bags of sand, placed in the car of a balloon for control of altitude and, less often, of attitude, or placed in an aircraft to control the position of the center of gravity.
3. anything that gives mental, moral, or political stability or steadiness:
   the ballast of a steady income.
4. Rail Transport gravel, broken stone, slag, etc., placed between and under the ties of a railroad to give stability, provide drainage, and distribute loads.
5. Electricity
   • Also called ballast resistor. a device, often a resistor, that maintains the current in a circuit at a constant value by varying its resistance in order to counteract changes in voltage.
   • a device that maintains the current through a fluorescent or mercury lamp at the desired constant value, sometimes also providing the necessary starting voltage and current.
6. Nautical, Idioms, Naval Terms in ballast, carrying only ballast; carrying no cargo.

v.t. 

7. Nautical, Naval Terms to furnish with ballast:
   to ballast a ship.
8. to give steadiness to;
   keep steady:
   parental responsibilities that ballast a person.

• Scandinavian; compare Old Danish, Old Swedish barlast, equivalent. to bar bare¹ + last load; see last⁴
• Middle Low German, perh. ultimately
• 1520–30

bal′last•er, n. 
bal•last•ic  (bə las′tik), adj. 

Collins Concise English Dictionary © HarperCollins Publishers::

ballast / ˈbæləst/ noun

1. any dense heavy material, such as lead or iron pigs, used to stabilize a vessel, esp one that is not carrying cargo
2. crushed rock, broken stone, etc, used for the foundation of a road or railway track
3. anything that provides stability or weight
4. a device for maintaining the current in a circuit

verb (transitive)

1. to give stability or weight to

Etymology: 16th Century: probably from Low German; related to Old Danish, Old Swedish barlast, literally: bare load (without commercial value), from bar bare, mere + last load, burden