sly /ˈslaɪ/ adjective


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

on the sly informal – in a secret way

  • They’ve been meeting each other on the sly. [=secretly]

Slyly adverb

  • The fox slyly went down the stairs.