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Definition of rock martin in US English:
rock martin
noun
Any of several martins and swallows that frequent cliffs, rocky outcrops, etc.; specifically (originally) the crag martin, Ptyonoprogne rupestris, or (in later use) the dark brown P. fuligula of Africa, which also nests on man-made structures.
Origin
Mid 19th century; earliest use found in The Penny Cyclopaedia.
