Definition of ballast noun from the Oxford Advanced Learner's Dictionary

     

    ballast

     noun
    noun
    BrE BrE//ˈbæləst//
     
    ; NAmE NAmE//ˈbæləst//
     
    [uncountable] Parts of boats and ships
     
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  1. 1heavy material placed in a ship or hot-air balloon to make it heavier and keep it steady See related entries: Parts of boats and ships
  2. 2a layer of stones that makes a strong base on which a road, railway/railroad, etc. can be built
  3. Word Origin mid 16th cent.: probably of Low German or Scandinavian origin.
See the Oxford Advanced American Dictionary entry: ballast