Yes, er is a Scrabble word!
...and is worth 2 points in Scrabble, and 2 points in Words with Friends
er
Noun
1. A trivalent metallic element of the rare earth group; occurs with yttrium
2. A room in a hospital or clinic staffed and equipped to provide emergency care to persons requiring immediate medical treatment
What Scrabble words can I make with the letters in er?
2 Letter Words