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'Try googling ' figures of speech' ? Indeed.It's metonymy and the word 'chair' is a metonym.The OED gives 'Stokes the name of the inventor...has , by metonymy, come to mean the trench mortar gun itself' and googled results include this from Shakespeare ; ' I must comfort the weaker vessel, as doublet and hose ought to show itself courageous to the petticoat' where the clothing stands for man and woman [As You Like It] and 'Washington' used for the US government.
Metaphor has an implicit comparison: He was a lion' meaning he was possessed of qualities like those of a lion. I don't think we are saying that a judge is like a piece of heavy wooden furniture, has its qualities, when we talk of the Bench (though I confess I can just see that in some judges, I hope the comparison is not universally made)