Yes, annex is a Scrabble word!
...and is worth 12 points in Scrabble, and 14 points in Words with Friends
annex
Verb
1. Take (territory) as if by conquest
2. Attach to
Noun
1. An addition that extends a main building
What Scrabble words can I make with the letters in annex?
3 Letter Words
2 Letter Words
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Words that can be created with an extra letter added to annex:
E:annexe