一所懸命

utmost effort, with all one's might, diligently

noun Rare #37,299
utmost effort A less common variant of 一生懸命; it refers to giving one's very best.
JA: 彼の一所懸命がチームを動かした。
EN: His utmost effort moved the team.

もっと一所懸命勉強するって約束したよね

You promised you'd study harder, remember?

一所懸命になって彼はそのに登った

He climbed the tree with all his might.

私だって一所懸命なんだ

I'm trying my best too.

— 自転車泥棒 (1948)

adverb Rare #37,300
with all one's might, diligently A traditional spelling of 一生懸命; often used to mean working or trying as hard as possible.
JA: 彼は一所懸命に勉強している。
EN: He is studying diligently.

もっと一所懸命勉強しなきゃいけないってトムに話した

I told Tom that he needed to study harder.

一所懸命働いて彼は成功した

He succeeded by working hard.