What do you call a word that is considered outdated or old-fashioned?

The term that describes a word regarded as outdated or old-fashioned is "archaism." This word specifically refers to terms, phrases, or linguistic forms that were once commonly used but have fallen out of everyday usage, often evoking a sense of history or a particular time period. In literature, an archaism might be employed to create a certain tone or atmosphere that harkens back to earlier styles of writing.

In contrast, a cliché refers to an expression or idea that has been overused to the point of losing its original meaning or impact. Hyperbole involves exaggerated statements or claims not meant to be taken literally, often used for emphasis or effect. The term imperative refers to a grammatical mood that expresses commands or requests, which is unrelated to the age or usage of words. Thus, "archaism" accurately captures the concept of outdated language.