Yes, fill is a Scrabble word!
...and is worth 7 points in Scrabble, and 9 points in Words with Friends
fill
Verb
1. Make full, also in a metaphorical sense
2. Become full
3. Occupy the whole of
4. Assume, as of positions or roles
5. Fill or meet a want or need
6. Appoint someone to (a position or a job)
7. Eat until one is sated
8. Fill to satisfaction
9. Plug with a substance
Noun
1. A quantity sufficient to satisfy
2. Any material that fills a space or container
What Scrabble words can I make with the letters in fill?
3 Letter Words
2 Letter Words