noun
Refers to a person actively involved in a social, political, or environmental movement. Neutral term; can be used for various causes.
彼女は環境保護の活動家として有名だ。
She is famous as an environmental activist.
その活動家は平和
The activist organized a peaceful protest.
Compound of 活動 (activity) and 家 (person who does something professionally or habitually). The word is a straightforward Sino-Japanese formation.