sly 
/ˈslaɪ/ adjective
sli·er or sly·er; sli·est or sly·est /ˈslaɪ/ adjective [also more sly; most sly] 1 : clever in a dishonest way
▪ a sly con man ▪ a sly scheme 2 : showing that you know a secret
▪ a sly wink/glance/smile
▪ a sly con man ▪ a sly scheme
▪ a sly wink/glance/smile
on the sly
informal : in a secret way
▪ They've been meeting each other on the sly. [=secretly]
▪ They've been meeting each other on the sly. [=secretly]
— sly·ly adverb
▪ He winked slyly.
▪ He winked slyly.
— sly·ness noun [noncount]
