Definition of lame duck by the Dictionary of American Idioms. lame duck idiom meaning. What does lame duck expression mean? How to use lame duck idiom? Example sentences with lame duck idiom. Originally Answered: What does the idiom 'a lame duck' mean? A person who occupies a position of authority, but cannot exercise that authority, usually because they're going to be replaced soon. It's commonly used to refer to American presidents in their second term. May 25, 2022 · The term “lame duck” dates back probably to the 18th century. More specifically, the London Stock Exchange, where a lame duck was a broker who had defaulted on their debt. For example when the Duchess of Devonshire lost a ton of money in stocks, Mary Berry wrote that the Duchess would be “posted up as a lame duck.”. This was around 1791..