Yes, bad is a Scrabble word!

Adverb

1. With great intensity (`bad' is a nonstandard variant for `badly')

2. Very much; strongly

Adjective

1. Having undesirable or negative qualities

2. Very intense

3. Feeling physical discomfort or pain (`tough' is occasionally used colloquially for `bad')

4. (of foodstuffs) not in an edible or usable condition

5. Feeling or expressing regret or sorrow or a sense of loss over something done or undone

6. Not capable of being collected

7. Below average in quality or performance

8. Nonstandard

9. Not financially safe or secure

10. Physically unsound or diseased

11. Capable of harming

12. Characterized by wickedness or immorality

13. Reproduced fraudulently

14. Not working properly

Noun

1. That which is below standard or expectations as of ethics or decency