| 1. | Also called underground railway. a railroad running through a continuous tunnel, as under city streets; subway. |
| 2. | (often initial capital letters ) U.S. History. (before the abolition of slavery) a system for helping fugitive slaves to escape into Canada or other places of safety. |
A network of houses and other places that abolitionists used to help slaves escape to freedom in the northern states or in Canada before the Civil War. The escaped slaves traveled from one “station” of the railroad to the next under cover of night. Harriet Tubman was the most prominent “conductor” on the Underground Railroad.