Pronunciation: (slī), [key]
—adj., sly•er or sli•er, sly•est or sli•est,
1. cunning or wily: sly as a fox.
2. stealthy, insidious, or secret.
3. playfully artful, mischievous, or roguish: sly humor.
on the sly, secretly; furtively: a tryst on the sly.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.