The phrase "threatening letter" is correct and can be used in written English.
For example: "The police received a threatening letter from the suspect."
Archives|BUTLER SUED FOR $10,000.; Charged With Falsely Accusing Man of Sending Threatening Letter.
BUTLER SUED FOR $10,000.; Charged With Falsely Accusing Man of Sending Threatening Letter.
Another threatening letter was sent in October, threatening to attack Tesco customers with pipe bombs if the demands were not met.
It's a threatening letter".
"I always have a threatening letter.
Cassius's estranged wife leaves Dana a threatening letter.
NW, after a threatening letter was opened about 11 30 a.m. in a basement mailroom.
They said he was also responsible for sending himself a threatening letter.
In February 1976, that attorney general, Bill Baxley, received a threatening letter.
At another school where a threatening letter was received, the principal protested.
Smollett said he had received a threatening letter at the "Empire" studio in Chicago.
