Metonymy is substituting one word for another based on close association rather than direct meaning.
Metonymy — Greek for 'a change of name' — replaces one term with another that is closely associated with it: 'the crown' for the monarchy, 'the White House' for the U.S. presidency, 'Hollywood' for the film industry. Unlike synecdoche, which requires a part-whole relationship, metonymy works through any kind of contiguity — physical, conceptual, institutional. Linguists from Roman Jakobson onward argued that metonymy and metaphor are the two fundamental modes of language: metaphor finds resemblance across categories, metonymy moves within them. Realist novelists rely on metonymy heavily — a worn glove evokes a marriage, a half-empty bottle evokes a man — and the device powers brand-building too: 'Kleenex' for tissue, 'Google' for search. It is the figure of speech most aligned with how memory itself indexes the world.