sly

US /slaɪ/
UK /slaɪ/
"sly" picture
1.

having or showing a cunning and deceitful nature

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He gave a sly grin as he hid the candy.
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The fox was known for its sly tricks.
:
cunningcraftywilyartfuldeceitful
2.

suggesting or characterized by a secret, knowing look or manner

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She gave him a sly wink across the room.
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There was a sly smile on his face, suggesting he knew more than he let on.
:
mischievousplayfulsecretiveknowingcovert
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on the sly