Unthinkability is a synonym of unthinkableness.
As nouns the difference between unthinkability and unthinkableness
is that unthinkability is the property of being unthinkable while unthinkableness is the property of being unthinkable.
unthinkability
English
Noun
(-)
The property of being unthinkable.
Synonyms
* unthinkableness
unthinkableness
English
Noun
(-)
The property of being unthinkable.
Synonyms
* unthinkability