A four-character idiom meaning to concentrate single-mindedly; to be deeply absorbed or focused without distraction.
彼は試験に向けて一心不乱に勉強した。
He studied single-mindedly for the exam.
職人は作業に一心不乱で、誰にも邪魔させなかった。
The craftsman was completely absorbed in his work and wouldn't let anyone disturb him.
瞑想中は一心不乱に呼吸に意識を向ける。
During meditation, focus your attention on the breath with undivided attention.