Kettlebells are heavy iron or steel balls with a thick handle on top, used in the gym to make muscles strong. You hold the handle and swing the weight, lift it to your shoulder, or press it over your head. Because the mass sits away from your hand, the swing feels different from a dumbbell — your whole body has to control it, not only your arm. One piece is a kettlebell; kettlebells is the plural, and that is how gyms often talk about them (“the kettlebells are over there”). They look a little like a kettle with a handle, which is how English named them. The training weight itself comes from Russia, where this shape is old; it became a fashionable gym tool in other countries later. They are sold from quite light to very heavy, and people of many ages use them, not only bodybuilders. The word belongs in sports and fitness talk. It is not a kitchen kettle, and it is not a bell you ring.