Meaning

noun an exercising weight; two spheres connected by a short bar that serves as a handle

noun an ignorant or foolish person

originFrom dumb (“silent”) + bell (“a resonating instrument”). The term "dumbbell" originated in 16th-century England to describe silent exercise apparatus used in practicing the motions of ringing church bells noiselessly. To aid them in the practice of their physically demanding vocation, bellringers originally used weighted ropes on fixed pulleys to mimic the motion of ringing a church bell; since…

Etymology from Wiktionary, CC BY-SA 3.0