ungenius

noun

1. A person who is not a genius.“For a heady moment I wanted to fling the notebook down and say to them: you write about geniuses and ungeniuses if you like, but don't teach me how to do it, I won't be able to do it anyway. I'd be better acting instead of you.”
2. Lack of genius.“Serenus Zeitblom, serene flower of the age, good-hearted, long-winded, the ungenius par excellence whose ungenius is his license to speak.”