misnomer

First recorded in 1425–75; late Middle English, from Anglo-French, noun use of Middle French mesnomer “to misname,” equivalent to mes- negating prefix + nomer “to name, call by name,” from Latin nōmināre; see mis-¹, nominate

Misnomer is not a fancy, more elevated word for mistake. Nor is it a synonym for misstatement, misconception, or misunderstanding. As the word's Latin etymon nōmināre (“to name”) tells us, a misnomer is a special kind of mistake: a wrong name. The consequences of a mistake can range from trivial to catastrophic—from typos to train wrecks. But a misnomer is often just embarrassing, like trying to impress a friend by referring to a Burgundy wine as a “Bordeaux.” Sometimes, however, what began as a misnomer has become a standard term: the game of Chinese checkers does not come from China; the funny bone is a nerve, not a bone; hay fever is not caused by hay and is not a fever; and a pregnant woman's morning sickness can occur at any time of day. Other kinds of mistakes or misunderstandings—giving a driver wrong directions, thinking that the earth is flat, drawing an erroneous conclusion—are not misnomers. In fact, the word misnomer when used to describe a behavioral mistake or a misperception of reality is itself a misnomer!

C15: via Anglo-Norman from Old French mesnommer to misname, from Latin nōmināre to call by name