Underground

noun

/ˈəndərˌɡround/

1. 1.

   a group or movement organized secretly to work against an existing regime.

   "I got involved with the French underground"

   Similar:

   resistance movement

   resistance

   illegal opposition

   partisans

   guerrillas

   freedom fighters

   Maquis

   • ​

2. 2.

   a group or movement seeking to explore alternative forms of lifestyle or artistic expression.

   "the late-sixties underground"