noun
radical; extremist
Refers to a person who advocates for drastic political or social change, often associated with revolutionary or extreme reform movements.
彼は急進主義者として知られ、政府の即時改革を求めている。
He is known as a radical, demanding immediate government reform.
過激派 refers to an extremist faction or group, often with a connotation of violent action, while 急進主義者 is a broader term for an individual advocating radical change, not necessarily violent.
保守主義者 is a conservative, someone who prefers traditional institutions and gradual change, the opposite of a radical.
Compound of 急進 (rapid progress) + 主義 (principle, -ism) + 者 (person). The term is a direct translation of the Western concept of 'radicalism'.