A piece of furniture, fixture, or equipment that is attached to or built into a building or vehicle; or the act of fitting something.
From 'fit' plus the noun suffix '-ment,' which creates nouns from verbs. British English especially uses this term for fixtures in homes and vehicles, dating to the 19th century.
British homeowners talk about 'fitted kitchens' and 'fitments' constantly—it's a precise word for all those cupboards and fixtures that are part of the house, not furniture you can move.
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