| unknown(obscure, dark, secret, hidden, concealed) |
| hush-hush(adjective, personal, clandestine, underground, confidential) |
| clandestine(adjective, secret, unknown, hidden, personal) |
| close(obscure, dark, unknown, hidden, concealed) |
| sealed(adjective, disclosed) |
| surreptitious(adjective, secret, unknown, hidden, concealed) |
| anonymous(adjective, choice, unknown) |
| arcane(obscure, unknown, clandestine, underground, unrevealed) |
| cryptic(cover, obscure, dark, unknown, hidden) |
| dormant |
| enigmatic(cover, obscure, dark, equivocal, ulterior) |
| esoteric(obscure, dark, secret, unknown, hidden) |
| hermetic(obscure, dark, secret, unknown, hidden) |
| occult(obscure, dark, unknown, hidden, imperceptible) |
| passive |
| restricted(clandestine, underground) |
| sneaking |
| top-secret(clandestine, underground) |
| top secret(expression, clandestine, underground) |
| unannounced(adjective, disclosed) |