Radical

徹底的な

tetteiteki na

(thoroughgoing)

抜本的な

bapponteki na

(favouring fundamental change)

根本的な

konponteki na

(pertaining to the basic or intrinsic nature of something)

急進派

kyūshinha

(person with radical opinions)

根

kon

(arithmetic: root (of a number or quantity))

累乗根

ruijōkon

(arithmetic: root (of a number or quantity))

部首

bushu

(linguistics: portion of a character that provides an indication of its meaning)