The word passable is an adjective. It describes something that can be passed.
One possible prefix for "passable" is "im", which would make the word "impassable".
The word passable does not have a prefix
unpassable
Is it passable fair fine good excellent splendid
not passable, blocked
It is not passable there is no evolving for it
respectable, tolerable, acceptable
Some looking like a woman
After I received a failing mark on my English paper, I spoke to the teacher and explained that, while I didn't think I deserved an "A", the work I did was certainly passable.
He plays a barely passable saxophone.
A mediocre grade is one that is barely passable.