We say “the kettle is boiling”

Metonym trades away literal accuracy for a different kind of truthfulness. We give to things the name of the enclosure that holds them all because we do not experience the parts discreetly but inseparably and because the parts themselves are sometimes inexpressible on their own. The names of all our important places are metonymical; it is one of the ways we contain their importances in words. A figure of speech gathers them together under one roof, into the same proximity that we feel in the living of them.

Ted Leeson, “Preface” from Inventing Montana (Skyhorse Publishing).