A mullion is a structural element which divides adjacent window units. Mullion may also refer to: Mullion (geology), a geological term for structures formed by extension Mullion, Cornwall, a village and parish in Cornwall, England Mullion, New South Wales, a locality in Australia Mullion Cove, a harbour and cove in Cornwall, England Mullion Creek, New South Wales, a town in Australia Mullion Island, a small island in Mount's Bay, Cornwall, England Mullion School, in Mullion, Cornwall, England People with the surname Annabel Mullion (born 1969), English actress