Yes, secret is a Scrabble word!

Adjective

1. Not open or public; kept private or not revealed

2. Conducted with or marked by hidden aims or methods

3. Not openly made known

4. Communicated covertly

5. Not expressed

6. Designed to elude detection

7. Hidden from general view or use

8. (of information) given in confidence or in secret

9. Indulging only covertly

10. Having an import not apparent to the senses nor obvious to the intelligence; beyond ordinary understanding

11. The next to highest level of official classification for documents

Noun

1. Something that should remain hidden from others (especially information that is not to be passed on)

2. Information known only to a special group

3. Something that baffles understanding and cannot be explained