Definition of "counterweight"

counterweight

noun
plural counterweights
1. A heavy mass of often iron or concrete, mechanically linked in opposition to a load which is to be raised and lowered, with the intent of reducing the amount of work which must be done to effect the raising and lowering. Counterweights are used, for example, in cable-hauled elevators and some kinds of movable bridges (e.g. a bascule bridge).
  Quotations
  Four 110-ton counterweights, one in each tower, make this feat possible by reducing the effective weight to be lifted to some 25 tons; but an additional 20 tons (a very heavy snow load) can be lifted if necessary.
  1960 May, “Talking of Trains: The new Kingsferry Bridge”, in Trains Illustrated, page 265
verb
third-person singular simple present counterweights, present participle counterweighting, simple past and past participle counterweighted
1. (transitive) To fit with a counterweight.
  Quotations
  Everything on the grid – all the backdrops and curtains, anything that has to move up and down from the fly-tower – has to be counterweighted.
  2018, Maggie Harcourt, Theatrical