Yes, sub is a Scrabble word!
...and is worth 5 points in Scrabble, and 7 points in Words with Friends
sub
Verb
1. Be a substitute
Noun
1. A large sandwich made of a long crusty roll split lengthwise and filled with meats and cheese (and tomato and onion and lettuce and condiments); different names are used in different sections of the United States
2. A submersible warship usually armed with torpedoes
What Scrabble words can I make with the letters in sub?
3 Letter Words
2 Letter Words