- underground movie,
- underground trolley,
Origin of underground railroad
"network of U.S. anti-slavery activists helping runaways elude capture," attested from 1847, but said to date from 1831 and to have been coined in jest by bewildered trackers after their slaves vanished without a trace. Originally mostly the term for escape networks in the (then) western states of the U.S.
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.
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.