A force or influence equally counteracting another.(noun)
American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Use "counterweight" in a sentence
"When a suitable counterweight is added at one end so that the reaction on one fulcrum is zero, the block can be spun asymmetrically 180 degrees about the other, giving a horizontal displacement (here's the basic physics)."
"This climate should produce an a important, long-term counterweight to the problems of our economy as a whole."
"Bahrain holds particular importance to Washington as the host of U.S. Navy's 5th Fleet, the main American counterweight to Iran's efforts to expand its military influence into the Gulf."