tumbler

Noun

• pigeon that executes backward somersaults in flight or on the ground

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

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

• a gymnast who performs rolls and somersaults and twists etc.

Related words

• Synonyms: 
  roller , tumbler pigeon