Yes, tall is a Scrabble word!
...and is worth 4 points in Scrabble, and 6 points in Words with Friends
tall
Adjective
1. Great in vertical dimension; high in stature
2. Lofty in style
3. Impressively difficult
4. Too improbable to admit of belief
Noun
1. A garment size for a tall person
What Scrabble words can I make with the letters in tall?
3 Letter Words
2 Letter Words