disapproval If you describe someone as sly, you disapprove of them because they keep their feelings or intentions hidden and are clever at deceiving people. She is devious and sly and manipulative = cunning
A sly look, expression, or remark shows that you know something that other people do not know or that was meant to be a secret. His lips were spread in a sly smile + slyly sly·ly Anna grinned slyly
marked by skill in deception; "cunning men often pass for wise"; "deep political machinations"; "a foxy scheme"; "a slick evasive answer"; "sly as a fox"; "tricky Dik"; "a wily old attorney"