Yes, digit is a Scrabble word!
...and is worth 7 points in Scrabble, and 8 points in Words with Friends
digit
Noun
1. One of the elements that collectively form a system of numeration
2. The length of breadth of a finger used as a linear measure
3. A finger or toe in human beings or corresponding body part in other vertebrates
What Scrabble words can I make with the letters in digit?
3 Letter Words
2 Letter Words