A Marilyn is a British hill that is separated from a higher hill by at least 500 feet (152 metres). This sense was coined in honour of the actress Marilyn Monroe (perhaps a pun on Munro, a type of Scottish hill) by Alan Dawson in his book The Relative Hills of Britain (ISBN 1852840684).
Marilyn (real name Peter Robinson) was a British pop singer of the early 1980s.