A tumbler is a drinking glass with a flat bottom and no handle or stem. Unlike a wine glass with its delicate stem or a coffee mug with its handle, a tumbler sits solidly on the table. You might drink water, juice, or milk from a tumbler at breakfast. The word comes from an old style of glass with a rounded or pointed bottom that would tumble over if you set it down, forcing drinkers to finish their beverage in one go.

The word also refers to an acrobat or gymnast who performs flips, rolls, and somersaults. A talented tumbler might execute a series of backflips across a mat. In gymnastics, tumbling describes floor exercise skills like handsprings and aerials that don't use apparatus like bars or beams.

Less commonly, a tumbler is a part inside a lock that must align correctly for a key to work. When you turn your key in a door, you're moving the tumblers into the right position.