ballast (bal|last)

noun

• 1heavy material, such as gravel, sand, or iron, placed in the bilge of a ship to ensure its stability: the hull had insufficient ballast
• a heavy substance carried in an airship or on a hot-air balloon to stabilize it and jettisoned when greater altitude is required: a forty kilo sandbag was used as ballast
• something providing stability or substance: the film is an entertaining comedy with some serious ideas thrown in for ballast

• 2gravel or coarse stone used to form the bed of a railway track or the substratum of a road: a thick layer of railway ballast
• a mixture of coarse and fine aggregate for making concrete.

• 3 [count noun] a passive component used in an electric circuit to moderate changes in current: ballasts are permanently wired into existing fixtures [as modifier]: ballast resistors

verb

• 1give stability to (a ship) by putting a heavy substance in its bilge: the vessel has been ballasted to give the necessary floating stability figurative people insufficiently ballasted with factual information

• 2form (the bed of a railway line or the substratum of a road) with gravel or coarse stone: the track was laid with rails and ballasted with earth