1. extreme and unreasoning enthusiasm, zeal, or devotion to a cause, belief, or activity

Examples

• Religious fanaticism led to violent conflicts throughout history.
• His fanaticism for the team made him attend every single game.
• The coach warned against the dangers of fitness fanaticism.
• Political fanaticism can blind people to reasonable compromise.
• Her fanaticism about cleanliness made living with her difficult.
• The documentary explored the rise of fanaticism in extremist groups.