Unfathomable means impossible to ever understand. For most people, the field of quantum mechanics is unfathomable. Fathoms are seafaring units of measure equaling about six feet. So something that is unfathomable is also immeasurable, especially when it comes to depth.

What does it mean if something is unfathomable?

: not capable of being fathomed: a : immeasurable. b : impossible to comprehend.

How do you use unfathomable in a sentence?

We are moving into depths that are unfathomable. It was almost unfathomable to me how she could get through it all as a pregnant woman. All this would be almost unfathomable to the generation before us. To many parents, teenage daughters are an unfathomable mystery.