| clandestine(adjective, secret, private, hidden) |
| surreptitious(adjective, secret, hidden, sneaky) |
| undercover(adjective, secret, private, hidden) |
| secret(adjective, private, hidden, sneaky) |
| hush-hush(adjective, secret, private, hidden) |
| underground(adjective, secret, hidden, covert) |
| covert(adjective, secret, private, hidden) |
| hidden(adjective, secret, private, sneaky) |
| stealth(adjective, secret, hidden, covert) |
| underneath(adjective, secret, hidden, covert) |
| on the QT(expression, adjective, idiom, secret, private) |
| private(adjective, secret, hidden, sneaky) |
| sub-rosa(adjective, secret, private, hidden) |
| underhand(adjective, secret, private, hidden) |
| concealed(adjective, secret, hidden, covert) |
| confidential(adjective, secret, hidden, covert) |
| creep(adjective, secret, hidden, covert) |
| incognito(adjective, secret, hidden, covert) |
| intelligence(adjective, secret, hidden, covert) |
| under cover(expression, adjective, secret, covert) |