Yes, tumblers is a Scrabble word!

Noun

1. A gymnast who performs rolls and somersaults and twists etc.

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

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. Pigeon that executes backward somersaults in flight or on the ground