tumbler

noun

1. 1

   pigeon that executes backward somersaults in flight or on the ground

2. 2

   a glass with a flat bottom but no handle or stem; originally had a round bottom

3. 3

   a movable obstruction in a lock that must be adjusted to a given position (as by a key) before the bolt can be thrown

4. 4

   a gymnast who performs rolls and somersaults and twists etc.