1. A piece of apparatus in the gym to flex the abdominal muscles: To use the abdominizer the user must lie on his or her back and rock backwards and forwards, exercising the abdominal muscles.

Also more generally, the abdominizer is one of various different types of equipment designed to strengthen the abdominal muscles.
2. An individual who performs exercises for the stomach muscles and also dresses in sportwear to show off the midriff: Jack was an abdominizer who loved to show the girls in the gym how terrific he looked!