Yes, strongest is a Scrabble word!

Adjective

1. Having strength or power greater than average or expected

2. Not faint or feeble

3. Having or wielding force or authority

4. Having a strong physiological or chemical effect

5. Immune to attack; incapable of being tampered with

6. Of good quality and condition; solidly built

7. Of verbs not having standard (or regular) inflection

8. Being distilled rather than fermented; having a high alcoholic content

9. Freshly made or left

10. Strong and sure