Plural of ballast; heavy materials (rocks, sand, water) loaded into ships to provide stability; devices or mechanisms for stabilizing or regulating.
From 'ballast' (Old Norse 'ballast' meaning 'bad load,' ironically the 'waste' weight that made ships workable). The term expanded to include metaphorical stabilizing forces in the 18th century.
Ballasts are one of those genius solutions hiding in plain sight—rocks and sand seem worthless until you realize they're the only thing preventing a ship from tipping over in the ocean.
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