Correct spelling, explanation: threat is a word that has Germanic origins and it already functioned in Old English and used to mean oppression. Threat also entered German and Dutch languages, but it had completely different forms back then as well as the meaning differed. In modern English threat is a noun used in formal and informal contexts.

Definition of threat:
1. noun – stating that someone will be hurt or something unpleasant will happen if the person doesn’t do something which he or she is asked for,
I heard from him a threat that he will commit suicide if I leave him.

Expressions with threat:
A few commonly used expressions with threat are as follows: security threat, death threat, and direct threat.
Please, do not switch your computer on and if it’s on, do not open any files as there is a serious security threat that our IT specialists have been working on.
As a prison guard, he gets a death threat almost every month, I don’t know how he can handle that.
People are panicking while the government clearly says that there isn’t any direct threat from the terrorists.

Incorrect spelling, explanation: a common spelling mistake is to write threat as threath, which is probably the result of the fact that many English words end with the -th ending, such as wreath, death, etc. However, in the case of threat the only correct spelling is without the -h letter in the last syllable.