From Gothish + -ness.
Gothishness (uncountable)
- (rare) The quality of being Gothish.
1882, Alice Weber, Two life-stories:[…] when his indignation had been stirred by what he considered her Gothishness, and want of hospitality to his best friend.
2017, Jen Agg, I Hear She's a Real Bitch:[…] if you took away the gothishness and heavy makeup.