一生懸命 (いっしょうけんめい) means with utmost effort, very hard, or with all one's might. It's an adverb used to describe doing something with intense dedication and energy, putting in maximum effort. For example: 彼は一生懸命勉強した。(He studied very hard.)

全ての力を使って、熱心に。例：一生懸命働く。