Yes, simple is a Scrabble word!

Adjective

1. Having few parts; not complex or complicated or involved

2. Easy and not involved or complicated

3. Apart from anything else; without additions or modifications

4. Exhibiting childlike simplicity and credulity

5. Lacking mental capacity and subtlety

6. (botany) of leaf shapes; of leaves having no divisions or subdivisions

7. Unornamented

Noun

1. Any herbaceous plant having medicinal properties

2. A person lacking intelligence or common sense