noun
1.
a short bar with a weight at each end, used for making the arm and shoulder muscles stronger
2.
( NAmE , informal ) a stupid person
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WORD ORIGIN
early 18th cent.: originally denoting an apparatus similar to that used to ring a church bell (but without the bell, so noiseless or “dumb”); sense 2 (dating from the 1920s) is an extended use by association with dumb stupid .