Is the word fascinate a synonym of grim?

No, "fascinate" and "grim" are not synonyms. They have completely opposite meanings.

* Fascinate means to attract and hold the attention of someone, often in a compelling or alluring way.

* Grim means serious, depressing, or bleak.

Here are some examples:

* Fascinate: The magician's tricks fascinated the audience.

* Grim: The news of the accident brought a grim silence to the room.

While something grim might be fascinating in a morbid way, the two words themselves are not interchangeable.