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Related to exercise ball: Swiss ball
A usually large, inflated plastic or rubber ball used especially for strengthening muscles and improving posture and balance, typically by leaning against or sitting on the ball and assuming different positions or by maneuvering the ball without using the hands. Also called gym ball, stability ball, Swiss ball.
American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.