2. Someone who is deeply dedicated to and involved with something; such as, a sport: I think Eliza is a real athletic fiend because she spends just about all of her time on the sports field.
In the small business, the people knew they had a friend in the senator who supported the tax relief that they needed if they were to survive the bad economic times.
The police said the fiend who was preying on youth in the park often met them by pretending to be their friend. In fact, the fiend was a fiend for skateboarding.