Fanatical (adjective)

1. Marked by excessive enthusiasm and often intense uncritical devotion.
2. Acting or tending to act with excessive zeal, especially in pursuit of religious or political causes.
3. Showing excessive enthusiasm or enthusiasm that is not reasonable.

Origin:

From french fanatique, from italian fanatico ("fanatic"), from latin fanaticus ("insane, frenzied, enthusiastic"), from fanum ("templ.e")

Examples:

1. He was a fanatical supporter of the team.
2. She was fanatical about her diet and exercise regimen.
3. The fanatical supporters of the political party were known for their extreme views.
4. The fanatical religious leader was known for his extreme views.
5. The fanatical group was known for their extreme actions.