| 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. |
Un·der·ground Railroad  (ŭn'dər-ground')  n.
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underground railroad
A secret network for moving and housing fugitives, as in There's definitely an underground railroad helping women escape abusive husbands. This term, dating from the first half of the 1800s, alludes to the network that secretly transported runaway slaves through the northern states to Canada. It was revived more than a century later for similar escape routes.