Yes, join is a Scrabble word!
...and is worth 11 points in Scrabble, and 14 points in Words with Friends
join
Verb
1. Become part of; become a member of a group or organization
2. Cause to become joined or linked
3. Come into the company of
4. Make contact or come together
5. Be or become joined or united or linked
Noun
1. The shape or manner in which things come together and a connection is made
2. A set containing all and only the members of two or more given sets
What Scrabble words can I make with the letters in join?
3 Letter Words
2 Letter Words