Sly \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.
--Fairfax.

2. Artfully cunning; secretly mischievous; wily.

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

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} (Zo["o]l.), the common sheldrake; -- so named
from its craftiness.

Syn: Cunning; crafty; subtile; wily. See {Cunning}.