having a hostile or deliberately frightening quality or manner

her mother had received a threatening letter

state one's intention to take hostile action against (someone) in retribution for something done or not done

how dare you threaten me?

the men threatened staff with a handgun

‘I might sue for damages,’ he threatened

cause (someone or something) to be vulnerable or at risk; endanger

a broken finger threatened his career

one of four London hospitals threatened with closure