So impossible or unbelievable that it's hard or impossible to imagine or think of something happening.
From 'in-' (not) plus 'conceivable' (able to be conceived), ultimately from Latin 'concipere' meaning 'to take in' or 'to grasp.' The word emerged in the 1600s.
The word 'inconceivable' became famous from the movie The Princess Bride, where a character says it constantly until told 'You keep using that word. I do not think it means what you think it means'—proving language is always evolving!
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