Yes, stemmer is a Scrabble word!

Noun

1. A worker who strips the stems from moistened tobacco leaves and binds the leaves together into books

2. A worker who makes or applies stems for artificial flowers

3. An algorithm for removing inflectional and derivational endings in order to reduce word forms to a common stem

4. A miner's tamping bar for ramming packing in over a blasting charge

5. A device for removing stems from fruit (as from grapes or apples)