| under-the-counter(hidden, sly, fraudulent) |
| under cover(expression, fickle, untrustworthy, unprincipled, sly) |
| under the table(expression, idiom, quietly, secretly, personally) |
| under wraps(expression, dishonest, cunning, deceitful, clandestine) |
| undercover(dishonest, cunning, deceitful, sly, clandestine) |
| underhand(adjective, dishonest, cunning, deceitful, fickle) |
| underhandedly(clandestine, quietly, secretly, personally, privately) |
| unethical(dishonest, cunning, deceitful, fickle, untrustworthy) |
| unfair(dishonest, cunning, deceitful, crooked, sneaky) |
| unjust(dishonest, cunning, deceitful, crooked, sneaky) |
| unobserved(quietly, secretly, personally, privately, furtively) |
| unscrupulous(dishonest, cunning, deceitful, crooked, sneaky) |
| wildcat(clandestine, secretly, furtively, slyly, underhandedly) |
| wily(dishonest, cunning, deceitful, sneaky, underhanded) |
| adulterine(fickle, untrustworthy, unprincipled, dirty-dealing) |
| adulterous(fickle, untrustworthy, unprincipled, dirty-dealing) |
| amoral(fickle, untrustworthy, unprincipled, dirty-dealing) |
| bigamous(fickle, untrustworthy, unprincipled) |
| changeful(fickle, untrustworthy, unprincipled, dirty-dealing) |
| cloak and dagger(expression, idiom, hidden, fraudulent) |