with all one's might; very hard; eagerly
Used to describe doing something with maximum effort, determination, or desperation. Can function as an adverb, adjectival noun, or noun.
彼は一生懸命勉強して、試験に合格した。
He studied very hard and passed the exam.
一生懸命走ったが、バスに間に合わなかった。
I ran as hard as I could, but I missed the bus.
彼女は一生懸命な人だから、きっと成功する。
She is a very hardworking person, so she will surely succeed.
She studied as hard as she could for the exam.
He's the kind of person who gives his all at everything he does.
My grandmother has always lived her life giving everything she has.
熱心 conveys enthusiasm or keen interest in something, while 一生懸命 focuses on exerting maximum effort regardless of enjoyment.
一生懸命 conveys earnest, almost desperate effort as if one's life depended on it, whereas 精一杯 simply means doing the maximum one is capable of.
一生懸命 stresses effort and hard work toward a goal, whereas 心を込めて stresses sincere, heartfelt feeling in doing something.
一生懸命 stresses giving one's utmost effort toward a goal, whereas せっせと focuses on the repetitive, busy manner of working.
一生懸命 highlights effort and hard work put into a task, whereas ひたすら focuses on undivided, repetitive concentration on one thing.