At the place of; at someone's home or establishment (borrowed from French, pronounced 'shay').
From Old French 'chez' meaning 'at the place of,' derived from Latin 'casa' (house). English borrowed it directly to sound elegant or refer to restaurants.
English speakers use 'chez' to sound sophisticated, but it's just French for 'at the house of'—saying 'chez Pierre' is basically just saying 'at Pierre's place' in another language.
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