Noah Webster's New International Dictionary of the English Language

1. (v. t.) Dexterous in performing an action, so as to escape notice; nimble; skillful; cautious; shrewd; knowing; -- in a good sense.

2. (v. t.) Artfully cunning; secretly mischievous; wily.

3. (v. t.) Done with, and marked by, artful and dexterous secrecy; subtle; as, a sly trick.

4. (v. t.) Light or delicate; slight; thin.

5. (adv.) Slyly.