hole-in-the-corner
Shady and secretive, typically to hide illicit activity. Primarily heard in UK. You can be sure there's some hole-in-the-corner activities going on in that private club.
hole-in-the-corner
or hole-and-corner
BRITISH, OLD-FASHIONEDIf you describe an activity or an event as hole-in-the-corner or hole-and-corner, you mean that it is kept secret, usually because it is dishonest or shameful. You deserve better than a hole-in-the-corner relationship like this. His visit was a hole-and-corner affair, and treated like a guilty secret.