Definitions:
heavy material, such as gravel, sand, or iron, placed in the bilge of a ship to ensure its stability

gravel or coarse stone used to form the bed of a railway track or the substratum of a road

a passive component used in an electric circuit to moderate changes in current

give stability to (a ship) by putting a heavy substance in its bilge

form (the bed of a railway line or the substratum of a road) with gravel or coarse stone