(This useful and informative post is brought to you by the words "ultra" and "man" -- causing translators to learn new and fascinating things since 1966)

Use of dumbbells originated in Tudor England, when athletes would use hand-held church bells of varying sizes for training purposes. As one might imagine, this could get quite cacophonous rapidly, and so they'd remove the clappers from the bells, rendering them silent, or "dumb". And thus the term "dumbbell" originated.