surreptitious
Definitions
Kept secret, especially because it would not be approved of.
Done, made, or acquired by stealth.
Examples
The spy made a surreptitious glance at the documents left on the desk.
She took a surreptitious bite of the cookie while her mother was distracted.
Their surreptitious meeting in the park was intended to avoid any unwanted attention.
Synonyms
secretive clandestine stealthy covert furtive sneaky undercover