Webster's English Dictionary

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ballast

1. bal.last \'bal-*st\ n [prob. fr. LG, of Scand origin; akin to Dan & Sw 
   barlast ballast; akin to] OE baer bare & to OE bl-st load - more at 
   LAST 1: a heavy substance used in a ship or balloon to improve its 
   stability  2: something that gives stability esp in character or conduct  
   3: gravel or broken stone laid in a railroad bed or used in making concrete 
2. ballast vt 1: to steady or equip with or as if with ballast  2: to fill 
   in (as a railroad bed) with ballast