| conspiratorial(clandestine, underground, undisclosed) |
| covered(clandestine, underground, undisclosed) |
| deep(clandestine, underground, undisclosed) |
| enigmatical(clandestine, underground, undisclosed) |
| esoteric(clandestine, underground, undisclosed) |
| for eyes only(expression, adjective, idiom, sensitive, sub-rosa) |
| hidden(clandestine, underground, undisclosed) |
| hidden away(expression, adjective, sensitive, sub-rosa) |
| imposturous |
| kept concealed(expression, adjective, sensitive, sub-rosa) |
| mysterious(clandestine, underground, undisclosed) |
| mystic(clandestine, underground, undisclosed) |
| mystical(clandestine, underground, undisclosed) |
| not for publication(expression, adjective, idiom, sensitive, sub-rosa) |
| obscure(clandestine, underground, undisclosed) |
| occult(clandestine, underground, undisclosed) |
| out-of-the-way(clandestine, underground, undisclosed) |
| private(clandestine, underground, undisclosed) |
| privileged(adjective, sensitive, sub-rosa) |
| recondite(clandestine, underground, undisclosed) |