on the sly
idiomPart ofsly
on the sly — idiom
1. Doing something in a secret way so that others do not know about it.
1.idiom
Definition
Doing something in a secret way so that others do not know about it.
Example
Maya ate a piece of cake on the sly before dinner.
Did you see Brian checking his phone on the sly during the meeting?
2. doing something secretly, especially when it is against the rules or disapproved
2.idiom
Definition
doing something secretly, especially when it is against the rules or disapproved of — for example, sneaking a cigarette when you have promised to quit, or meeting someone you are not supposed to see.
Example
Mark had been smoking on the sly, though he promised his family he had quit.
The two friends would exchange notes on the sly during the boring history class.