on the sly
Without anyone knowing
On the sly means secretly or covertly, especially when doing something one shouldn't: He'd been meeting her on the sly for months.
The phrase suggests deception or concealment from others who would disapprove: She was eating candy on the sly while supposedly dieting.
- hush-hushHighly confidential matter
- hush hushExtremely secret, concealed
- stealthilyIn a covert manner
- furtiveSecretive and sly
- surreptitiouslyIn a hidden manner
in secret · clandestine · unbeknownst · behind someone's back · covert · sub rosa · hidden · secretive · under the radar · on the quiet · sneaky · incognito · low-key · cloak-and-dagger · wink · down low · flying under the radar · underhanded
on the slyopenly
Without hiding anything
in the open · publicly · out in the open · in public · in plain sight
on the slyhonestly
In a truthful manner
forthrightly · on the level · candidly · on the up and up · straightforwardly