misnomer
Definitions
A wrong or inaccurate name or designation.
The use of a term that is misleading or inappropriate.
Examples
Calling the tiny dog a 'giant' was clearly a misnomer.
The term 'common cold' is a bit of a misnomer, as it is caused by a virus rather than low temperatures.
It is a misnomer to label the small room a 'master suite' when it barely fits a bed.
Synonyms
misnaming malapropism mislabeling error inaccuracy solecism misidentification