一大決心 いちだいけっしん Meanings Noun, する verb momentous (crucial) decision Kanji 一 one. Read as イチ. 大 big. Read as ダイ. 決 decide. Read as ケツ. 心 heart. Read as シン. Common phrases 一大決心をする Word lists Yojijukugo (四字熟語) Jinuma: Japanese Dictionary · Word lists