Yes, ill is a Scrabble word!

Adverb

1. (`ill' is often used as a combining form) in a poor or improper or unsatisfactory manner; not well

2. Unfavorably or with disapproval

3. With difficulty or inconvenience; scarcely or hardly

Adjective

1. Affected by an impairment of normal physical or mental function

2. Resulting in suffering or adversity

3. Distressing

4. Indicating hostility or enmity

5. Presaging ill fortune

Noun

1. An often persistent bodily disorder or disease; a cause for complaining