There's probably a "correct" answer to this question, but we'd rather see what you can come up with. A reader emails,
I have enjoyed your website for a long time. We have a question that we haven't been able to solve by checking the internet, so we thought we'd come to you. Is a member of co-op a co-oper? A co-operator? Any help you can give us would be appreciated.Your co-operation, please, in the comments.