dumbbell (n.)youdaoicibaDictYouDict[dumbbell 词源字典]
"weighted bar used for exercise," 1711, originally an apparatus like that used to ring a church bell, but without the bell (hence dumb); used for exercise but sometimes also to practice ringing changes. Figurative sense of "blockhead, stupid person" attested by 1918, American English college slang.[dumbbell etymology, dumbbell origin, 英语词源]