sly /slai/ I. adj. 狡猾的：She had a sly personality. 她个性狡诈。‖II. n. 用于习语on the sly秘密地，偷偷地：He drives his mother’s car on the sly while she’s at work.妈妈上班时，他偷偷地开了她的车。She was drinking on the sly.她偷偷地喝酒。