From Longman Dictionary of Contemporary Englishgo undergroundgo undergroundSECRETto start doing something secretly, or hide in a secret place The ANC was forced to go underground when its leaders were arrested. → underground
Examples from the Corpus
go underground• A few days later, Valenzuela went underground.• But some of the activity has gone underground.• If company policies are too stringent or punitive, couples simply go underground.• Instead of changing its policies, however, the government went underground.• The redevelopment proposals put forward for the site at first envisaged that all the shopping should go underground.• Delvalle went underground but continued to be recognized by the United States.• Like the Sleepers of Ephesus, ideas go underground for a few centuries to re-emerge when times are more propitious.• Fresh air bases were set up in Bank Mine and a team of brave and dedicated doctors went underground to assist.• Denkins went underground to escape police. 