tumbler

(noun) a gymnast who performs rolls and somersaults and twists etc..

(noun) a glass with a flat bottom but no handle or stem; originally had a round bottom.

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

(noun) pigeon that executes backward somersaults in flight or on the ground. Synonyms: roller, tumbler pigeon.