Which term describes a name that is wrongly or unsuitably applied?

The term that accurately describes a name that is wrongly or unsuitably applied is "misnomer." A misnomer typically refers to a designation that is inappropriate or incorrect, often arising from a misunderstanding or misuse of the term. For instance, referring to a koala bear as a bear is a misnomer because koalas are not bears; they belong to a completely different group of marsupials.

In contrast, nomenclature refers broadly to a system of naming, particularly within scientific disciplines, while taxonomy deals specifically with the classification of organisms, including naming them according to established systematics. Designation is a more general term referring to the act of appointing or assigning a name or label, but it does not imply the inappropriate application of that name. Therefore, "misnomer" is the term that best encapsulates the concept of an incorrectly applied name.