Here are some synonyms for inconceivable:
* Unthinkable
* Unbelievable
* Implausible
* Impossible
* Imaginable
* Absurd
* Outrageous
Examples:
* "The idea of a robot writing a novel seemed inconceivable just a few years ago."
* "It was inconceivable to her that her son would ever do anything to harm someone."
* "The sheer scale of the disaster was inconceivable."
Note: The word "inconceivable" is often used in a humorous way, particularly in the context of the movie "The Princess Bride." In this case, it can be used to mean something that is simply absurd or ridiculous.