要害堅固 ようがいけんご Meanings Noun, の-adjective (a fortress being) impregnable; unassailable Kanji 要 need. Read as ヨウ. 害 harm. Read as ガイ. 堅 firm. Read as ケン. 固 solid. Read as コ. Word lists Yojijukugo (四字熟語) Jinuma: Japanese Dictionary · Word lists