General Antonyms:
* Boring
* Dull
* Monotonous
* Tedious
* Uninteresting
* Uninspiring
* Repelling
* Unengaging
More specific antonyms:
* Repulsive: If something is fascinating because of its beauty, the antonym could be repulsive.
* Ordinary: If something is fascinating because of its uniqueness, the antonym could be ordinary.
* Unremarkable: If something is fascinating because of its significance, the antonym could be unremarkable.
Example:
* "The lecture was fascinating, I couldn't take my eyes off the speaker." (Antonym: boring)
* "The museum exhibit was fascinating, with artifacts from ancient civilizations." (Antonym: uninteresting)
Choose the antonym that best fits the specific situation and the intended meaning.