| under cover(expression, adjective, adverb, secret, fickle) |
| under the table(expression, idiom, sensitive, quietly, personally) |
| under wraps(expression, dishonest, secret, clandestine, underground) |
| underground(adjective, obscure, unusual, deep, mysterious) |
| underhand(adjective, dishonest, cunning, deceitful, secret) |
| underhanded(dishonest, cunning, deceitful, clandestine, underground) |
| underhandedly(clandestine, quietly, secretly, personally, privately) |
| unethical(dishonest, cunning, deceitful, fickle, untrustworthy) |
| unforthcoming(reserved, mysterious, private, reticent, taciturn) |
| unobserved(quietly, secretly, personally, privately, furtively) |
| unofficial(sensitive, secret, private, confidential, eyes-only) |
| veiled(obscure, secret, private, unknown, hidden) |
| wildcat(clandestine, secretly, furtively, slyly, underhandedly) |
| withdrawn(reserved, mysterious, private, reticent, taciturn) |
| zipped(mysterious, private, reticent, taciturn, covert) |
| QT(unknowing, hermetical, unbriefed) |
| abstruse(obscure, unknown, clandestine, underground, undisclosed) |
| adulterine(fickle, untrustworthy, unprincipled, dirty-dealing) |
| adulterous(fickle, untrustworthy, unprincipled, dirty-dealing) |
| aloof(reserved, reticent, taciturn) |