Definify.com
Webster 1913 Edition
Frightfulness
Fright′ful-ness
,Noun.
 The quality of being frightful. 
Webster 1828 Edition
Frightfulness
FRIGHTFULNESS
,Noun.
  Definition 2025
frightfulness
frightfulness
English
Noun
frightfulness (usually uncountable, plural frightfulnesses)
- The quality of being frightful.