| sly(clandestine, underground, undisclosed) |
| sneaky(clandestine, underground, undisclosed) |
| stealthy(clandestine, underground, undisclosed) |
| sub-rosa(adjective, close, sensitive, clandestine, underground) |
| surreptitious(clandestine, underground, undisclosed) |
| top secret(expression, close, sensitive, inside, clandestine) |
| unacknowledged(adjective, close, sensitive, inside, clandestine) |
| under-the-table(adjective, sensitive, clandestine, underground, undisclosed) |
| under the table(expression, adjective, close, sensitive, inside) |
| under wraps(expression, adjective, sensitive, clandestine, underground) |
| underhanded(clandestine, underground, undisclosed) |
| sneak(close, inside, clandestine, underground, undisclosed) |
| abstruse(clandestine, underground, undisclosed) |
| ambiguous(clandestine, underground, undisclosed) |
| arcane(clandestine, underground, undisclosed) |
| buttoned up(expression, adjective, sensitive, sub-rosa) |
| clandestine(underground, undisclosed) |
| cloak-and-dagger(clandestine, underground, undisclosed) |
| closet(clandestine, underground, undisclosed) |
| clouded(clandestine, underground, undisclosed) |