Which term refers to the use of one term that is closely associated with another to mean the other?

The correct term for the use of one word or phrase that is closely associated with another to represent that other idea is metonymy. This figure of speech relies on the relationship between the two concepts, where one word replaces another based on a contextual or conceptual association rather than a direct relationship.

For instance, when someone refers to the "White House" to mean the U.S. President or the U.S. administration, they are using metonymy. This is effective in conveying meaning and making language more evocative and relatable.

The other terms do not apply in this context. Synecdoche refers specifically to a figure of speech in which a part represents the whole or vice versa, such as saying "all hands on deck" to refer to sailors. An oxymoron combines contradictory or opposing ideas, like "jumbo shrimp." Antonymy describes the relationship between words with opposite meanings, such as "hot" and "cold." Therefore, metonymy is the appropriate choice for the definition provided.