fanatic.

A person whose commitment to a cause or interest is extreme or unyielding.

Use it for

Words that belong together

• a political fanatic
• a fitness fanatic

On the page

The pamphlet called her a fanatic because she refused every compromise.

He was a fitness fanatic in the affectionate language of friends, not a threat to anyone.

Usage notes

Primary category: psychological / character. Forms: Singular fanatic; plural fanatics. Legacy lexical fields mirror sense 1 only. Use numbered sense fields for all meanings.