| on the sly(expression, idiom, clandestine, quietly, personally) |
| privately(clandestine, quietly, secretly, personally, slyly) |
| privily(quietly, secretly, personally, privately, furtively) |
| quietly(secretly, personally, privately, furtively, slyly) |
| secretly(clandestine, slyly, underhandedly, surreptitiously) |
| slyly(clandestine, quietly, secretly, personally, privately) |
| stealthily(clandestine, quietly, secretly, personally, privately) |
| sub rosa(expression, clandestine, quietly, personally, privately) |
| surreptitiously(clandestine, quietly, secretly, personally, privately) |
| under-the-counter(hidden, sly, fraudulent) |
| under the table(expression, idiom, quietly, secretly, personally) |
| under wraps(expression, hidden, clandestine, fraudulent, secretly) |
| undercover(sly, clandestine, fraudulent, secretly, furtively) |
| underhandedly(clandestine, quietly, secretly, personally, privately) |
| unobserved(quietly, secretly, personally, privately, furtively) |
| wildcat(clandestine, secretly, furtively, slyly, underhandedly) |
| cloak and dagger(expression, idiom, hidden, fraudulent) |
| concealed(hidden, fraudulent) |
| fraudulent(hidden, sly) |
| furtive(hidden, fraudulent) |