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Meaning of underground railroad

un'derground rail'road

Pronunciation: [key]
  1. Also calleda railroad running through a continuous tunnel, as under city streets; subway.
  2. (often caps.)(before the abolition of slavery) a system for helping fugitive slaves to escape into Canada or other places of safety.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.