不用心 ぶようじん Also written ふようじん, 無用心 Meanings な-adjective, Noun unsafe; insecure; careless; dangerous; incautious; imprudent Kanji 不 un-. Read as ブ. 用 use. Read as ヨウ. 心 heart. Read as シン. Example sentences なんて不用心なんだ。How could you be so careless? Jinuma: Japanese Dictionary · Word lists