v.1. To bend or fold something back upon itself at the middle: We had to double over the invitations to fit them in the envelopes. I doubled my ticket over and stuck it in my pocket.
2. To bend or fold in half at the middle: These lawn chairs double over so you can store them in a small space.
3. To cause someone to bend over from the waist: The bad smell doubled the kids over when they entered the school. The comedian's funny jokes doubled us over.
4. To bend over from the waist: When he got the bad news, he just doubled over. She was so sick from the flu that she doubled over.