A worker or tradesperson who applies compo (plaster or composite material) to buildings, particularly for repairs and decorative work.
From 'compo' plus the agent suffix '-er', creating a term for someone who works with the material. This is primarily British trade vocabulary.
A 'compoer' is part of the specialized vocabulary that exists in trades but rarely appears in formal English—it's a perfect example of how professional communities create their own precise terminology for specific jobs.
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