misassumption

noun

mis·​as·​sump·​tion ˌmis-ə-ˈsəm(p)-shən 

plural misassumptions

: something that is incorrectly assumed to be granted or true : a mistaken assumption

I shudder to think of how much margarine I ate growing up on the misassumption that it was somehow healthier.

—Richard T. Bosshardt

misassume

ˌmis-ə-ˈsüm 

transitive verb

misassumed; misassuming

… a lot of boys get shunted into programs that misassume what they can and can't do …

—Richard Whitmire

Word History

First Known Use

1860, in the meaning defined above