on the sly

Idioms and Phrases

Furtively, secretly, as in She's always eating cookies on the sly . The adjective sly , which means “cunning” or “crafty,” is here used as a noun. [c. 1800]

Example Sentences

Opening the case, prosecutor Naeem Valli said Connolly also sent a message saying she intended to work her notice period as a childminder "on the sly" - despite being de-registered.

From BBC

“Beatrice is seeing Gideon McSorley on the sly!”

From Literature

In contravention of their oath, the men make advances on the sly and the wary women prank them to test their mettle.

From New York Times

"On the sly," Onishi said, someone like that can "listen to the podcast, watch the YouTube channel" and come to understand "the other ways people think" and "why they left."

From Salon

We were forbidden to speak Urdu, but my mother still taught us on the sly.

From New York Times

Related Words

• clandestine
• covert
• furtive
• hush-hush
• unauthorized