Artfully dextrous in performing things secretly, and escaping observation or detection; usually implying some degree of meanness; artfully cunning; applied to persons; as a sly man or boy.

Done with artful and dextrous secrecy; as a sly trick.

Marked with artful secrecy; as sly circumspection.

Secret; concealed. Envy works in a sly imperceptible manner.