Which figure of speech compares two unlike things by saying one is the other?

The correct answer is a metaphor, which is a figure of speech that directly compares two unlike things by stating that one is the other, thereby implying a deeper connection or similarity between them. This type of comparison does not use words like "like" or "as," which are typically found in similes. For example, saying "Time is a thief" suggests that time steals moments from our lives, showcasing its impact in a vivid way.

Metonymy involves substituting the name of one thing with something closely associated with it, rather than drawing a direct comparison. Similes also compare two unlike things but do so using "like" or "as," which differentiates them from metaphors. Apostrophe is a figure of speech where a speaker addresses an absent person, an abstract idea, or a thing, rather than making a comparison between unlike entities.

Understanding metaphors enriches the interpretation of literature and enhances one's ability to appreciate the nuances of language.