novercaphobia 

An irrational and debilitating fear of your step-mother.

He didn't want his father to get a partner, his novercaphobia would drive him to move away from him if he did.

novercaphobia by tvfetish September 24, 2021

novicaphobia 

The irrational fear of one's mother-in-law.

She was hindered from visiting her mother by her husband's novicaphobia.

novicaphobia by postulio89 September 8, 2007