From Longman Dictionary of Contemporary Englishballastbal‧last /ˈbæləst/ noun [uncountable] 1 TTWheavy material that is carried by a ship to make it more steady in the water2 TTAmaterial such as sand that is carried in a balloon so that it can be thrown out to make it rise3 TTRa layer of broken stones that a road or railway line is built on
Examples from the Corpus
ballast• I bought nine fluorescent light fixtures-bulbs, ballast, and wire.• The reactions and thrust of each deck is taken on elastomeric bearings and by ballast walls.• The flooding followed a 10-15 o list to port, due to water pouring into the forward ballast tanks.• They got the ballast out and loaded it into skips and the loco brought it along the line to the plant.• Many nights my bunk was blanketed by blueprints as I worked my way through the schematics of the variable ballast system.• Yet when he spoke of himself, his gaze frequently wandered, as though in search of visual ballast.• With ballast weights at each blade tip, the whirling rotor system had tremendous inertia.Origin ballast (1500-1600) Probably from Low German 