| recondite(adjective, obscure, unknown, clandestine, underground) |
| restricted(clandestine, underground, undisclosed) |
| reticent(obscure, deep, unknown, clandestine, underground) |
| retired(obscure, deep, unknown, clandestine, underground) |
| secluded(obscure, unknown, clandestine, underground, undisclosed) |
| secretive(clandestine, underground, undisclosed) |
| shrouded(obscure, unknown, clandestine, underground, undisclosed) |
| sly(clandestine, underground, undisclosed) |
| sneak(close, inside, clandestine, underground, undisclosed) |
| sneaky(adjective, clandestine, underground, undisclosed) |
| sub-rosa(close, sensitive, clandestine, underground, undisclosed) |
| top secret(expression, close, sensitive, inside, clandestine) |
| unacknowledged(close, sensitive, inside, clandestine, underground) |
| under-the-table(sensitive, clandestine, underground, undisclosed, sub-rosa) |
| under false pretense(expression, idiom, close, sensitive, clandestine) |
| under the radar |
| unenlightened(obscure, deep, unknown, clandestine, underground) |
| unfrequented(obscure, deep, unknown, clandestine, underground) |
| unpublished(obscure, deep, unknown, clandestine, underground) |
| unseen(obscure, unknown, clandestine, underground, undisclosed) |