noun
radicalist
A person who advocates for radical political or social change. This is a direct loanword and is used similarly to the English term.
彼は若い頃、ラジカリストとして活動していた。
In his youth, he was active as a radicalist.
過激派 is a more common native Japanese term for 'radical faction' or 'extremists', while ラジカリスト is a less frequent loanword focusing on the individual advocate.
Borrowed from English 'radicalist'.