/ slaɪ; NAmE / adjective
1.
( disapproving ) acting or done in a secret or dishonest way, often intending to trick people
SYN cunning :
a sly political move
( humorous )
You sly old devil! How long have you known?
2.
[ usually before noun ] suggesting that you know sth secret that other people do not know
SYN knowing :
a sly smile / grin / look / glance, etc.
► slyly adverb :
He glanced at her slyly.
► sly·ness noun [ U ]
•
IDIOMS
- on the sly
••
WORD ORIGIN
Middle English (also in the sense dexterous ): from Old Norse slœgr cunning, originally able to strike from the verb slá .