Wearing or clothed in a greatcoat; dressed in a long, heavy overcoat.
From 'greatcoat' + '-ed' (participial/adjectival suffix); this creates an adjective by adding '-ed' to the noun, meaning 'dressed in or wearing the stated garment.'
English allows this '-ed' pattern with almost any clothing noun (a 'suited man,' a 'jacketed figure'), which gives writers perfect shorthand for describing how someone is dressed in historical fiction or formal descriptions.
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