dumb·bell 
(dŭmbĕl′)
(dŭmbĕl′)n.
1. A weight consisting of a short bar with a metal ball or disk at each end that is lifted for muscular development and exercise.
2. Slang A stupid person; a dolt.
[From an apparatus similar to that used in ringing a church bell, but without the bell, used for practice or physical exercise.]