Yes, tar is a Scrabble word!
...and is worth 3 points in Scrabble, and 3 points in Words with Friends
tar
Verb
1. Coat with tar
Noun
1. Any of various dark heavy viscid substances obtained as a residue
2. A man who serves as a sailor
What Scrabble words can I make with the letters in tar?
3 Letter Words
2 Letter Words