What is it called when the name of one object is substituted for another closely related to it?

The term that refers to substituting the name of one object for another closely associated with it is metonymy. This literary device leverages the relationship between the two entities, allowing the name of one to evoke the concept of the other. For example, using "the White House" to refer to the U.S. President or their administration exemplifies metonymy, as the White House is a building closely associated with the executive branch of government.

In contrast, synecdoche, while also a figure of speech, specifically involves substituting a part for the whole or vice versa, such as referring to workers as “hands.” Alliteration, a separate literary device, refers to the repetition of the initial consonant sounds in a series of words, typically in close proximity, and imagery pertains to the use of descriptive language to create sensory experiences in the reader’s mind. These distinctions clarify why metonymy is the correct choice in this context.