sub·ter·ra·nean
| \ ˌsəb-tə-ˈrā-nē-ən
, -nyən\
variants:
or less commonly subterraneous \ ˌsəb-tə-ˈrā-nē-əs
, -nyəs \
1
: being, lying, or operating under the surface of the earth
2
: existing or working in secret : hidden
a subterranean network of criminals