To remove decorations from something or to strip away ornamental features from a space or object.
From the prefix 'de-' (meaning to remove or reverse) combined with 'decorate' (from Latin 'decorare' meaning to adorn), following the standard English pattern of adding 'de-' to create an opposite action.
English is wonderfully logical in this way—if you can decorate something, you can literally un-decorate it by adding 'de-' to the front, though we usually just say 'strip' or 'remove decorations.'
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