Refers to strict, literal adherence to basic principles, especially in religion or ideology. Often used in compounds like イスラム原理主義 (Islamic fundamentalism).
Fundamentalism can sometimes lead to extremist actions.
He criticized market fundamentalism.
根本主義 is a less common synonym for religious fundamentalism, while 原理主義 is the standard term and can also apply to non-religious contexts like market fundamentalism.
Islamic fundamentalism
Compound of 原理 (principle) and 主義 (doctrine, -ism). A Meiji-era calque from Western languages, likely from English 'fundamentalism' or German 'Fundamentalismus'.