tenacious
adj.adj. refusing to give up or let go of something. You use this to describe someone who keeps trying very hard even when things are difficult.
adj. persistent in maintaining an adherence to a goal, belief, or physical grip. Often used to describe a person's character or the strength of a physical hold.
She is a tenacious student who never stops asking questions.
The lawyer's tenacious questioning eventually forced the witness to admit the truth about the missing documents.
Despite facing repeated rejections from every major publisher, the author remained tenacious, eventually securing a deal that launched her career into the bestseller lists.
From Latin tenāx (“holding fast, clinging”), from tenēre (“to hold”), + -ious.
Often used predicatively after 'be' or 'remain', or attributively before a noun like 'grip', 'defense', or 'advocate'.