ballast

[bal-uhst]
noun
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.
gravel, broken stone, slag, etc., placed between and under the ties of a railroad to give stability, provide drainage, and distribute loads.
5.
Electricity.
a.
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.
b.
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.
verb (used with object)
6.
to furnish with ballast: to ballast a ship.
7.
to give steadiness to; keep steady: parental responsibilities that ballast a person.
Idioms
8.
in ballast, Nautical. carrying only ballast; carrying no cargo.

Origin:
1520–30; < Middle Low German, perhaps ultimately < Scandinavian; compare Old Danish, Old Swedish barlast, equivalent to bar bare1 + last load; see last4

ballaster, noun
ballastic [buh-las-tik] , adjective
overballast, verb (used with object)
subballast, noun
underballast, verb (used with object)
Dictionary.com Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2014.
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World English Dictionary
ballast (ˈbæləst)
 
n
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.  coarse aggregate of sandy gravel, used in making concrete
4.  anything that provides stability or weight
5.  electronics a device for maintaining the current in a circuit
 
vb
6.  to give stability or weight to
 
[C16: probably from Low German; related to Old Danish, Old Swedish barlast, literally: bare load (without commercial value), from bar bare, mere + last load, burden]

Collins English Dictionary - Complete & Unabridged 10th Edition
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Etymonline
Word Origin & History

ballast
"heavy material used to steady a ship," 1520s, from M.E. bar "bare" (in this case "mere") + last "a load, burden," or borrowed from identical terms in North Sea Gmc. and Scand. (cf. O.Dan. barlast, 14c.). Du. balg-last "ballast," lit. "belly-load," is a folk-etymology corruption.
Online Etymology Dictionary, © 2010 Douglas Harper
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Example sentences
For some reason, the starboard ballast tanks have failed to refill properly,
  and the ship has abruptly lost its balance.
In those days, the precious metal was sometimes used as heavy ballast to help
  keep a ship steady.
Ballast water is carried in a ship's hold for increased stability.
Jellies have hitched free rides all over the world, frequently traveling in the
  ballast water of ships.
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