Definition:
An "extremist" is a noun that refers to a person who holds very strong, often radical beliefs or opinions that are far from what most people think or believe. These beliefs can be about politics, religion, or other important issues. The word can also be used as an adjective to describe opinions or actions that are far beyond what is considered normal or acceptable.
As a Noun: Use "extremist" to describe someone with extreme views.
As an Adjective: Use "extremist" to describe actions or opinions.
Extremism (noun): The belief in or support for extreme measures or views.
Extremist (adjective): Pertaining to extreme views.
While the primary meaning relates to strong beliefs, "extremist" can also be applied in a more general sense to describe any person or action that goes to great lengths or extremes in any area (not just politics or religion).
"Crossing the line": This means going beyond what is considered acceptable. It can relate to extremist actions.
"Take a hard line": This means to have a strict or severe position on an issue, often associated with extremist views.