Underground railway and Underground railroad

Underground railway noun - Secret aid to escaping slaves that was provided by abolitionists in the years before the American Civil War.

Underground railroad is a synonym for underground railway. In some cases you can use "Underground railroad" instead a noun phrase "Underground railway".

Underground railroad noun - Secret aid to escaping slaves that was provided by abolitionists in the years before the American Civil War.

Underground railway is a synonym for underground railroad in secret cooperative network topic. You can use "Underground railway" instead a noun phrase "Underground railroad".