1957, Manny Farber, "Underground Films", in Robert Walsh (ed.) Negative Space: Manny Farber on the movies (1998), p. 27,
The excess that is so noticeable in Stevens's brawl is absent in the least serious undergrounder, […]
1985, Abe Peck, Uncovering the Sixties: The Life and Times of the Underground Press, p. 51,
Street people, day-trippers, and tourists pushed the paper's circulation to 117,000, the largest any community undergrounder would reach.
A person who dwells underground.
One who is part of a secret or underground society or subculture.