Archaic or dialectal adjective, possibly meaning 'having a copple' or 'hill-like'; exact meaning is uncertain and the word is no longer in use.
Past participle or adjective form derived from copple with the addition of -ed, following Middle English word formation patterns, though the base word itself is now obsolete.
Words like coppled show how Old English speakers would create descriptive terms by adding endings to nouns—if a place had a distinctive hill, calling it 'coppled' made perfect sense to them, but we've lost that linguistic flexibility.
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