Sly, adv. Slyly. [Obs. or Poetic] Spenser.

Sly (?), a. [Compar. Slier (?) or Slyer; superl. Sliest or Slyest.] [OE. sli, slegh, sleih, Icel sl?gr, for sl?gr; akin to Sw. slug, Dan. slu, LG. slou, G. schlau; probably to E. slay, v.t.; cf. G. verschlagen sly. See Slay, v. t., and cf. Sleight.] 1. Dexterous in performing an action, so as to escape notice; nimble; skillful; cautious; shrewd; knowing; -- in a good sense.

Be ye sly as serpents, and simple as doves.
Wyclif (Matt. x. 16).

Whom graver age
And long experience hath made wise and sly.

2. Artfully cunning; secretly mischievous; wily.

For my sly wiles and subtle craftiness,
The litle of the kingdom I possess.

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

Envy works in a sly and imperceptible manner.
I. Watts.

4. Light or delicate; slight; thin. [Obs.]

By the sly, or On the sly, in a sly or secret manner. [Colloq.] "Gazed on Hetty's charms by the sly." G. Eliot. -- Sly goose (Zoöl.), the common sheldrake; -- so named from its craftiness.

Syn. -- Cunning; crafty; subtile; wily. See Cunning.