The Collaborative International Dictionary of English v.0.48:
Sly \Sly\, a. [Compar. Slieror 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
1. Dexterous in performing an action, so as to escape notice;
nimble; skillful; cautious; shrewd; knowing; -- in a good
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. --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.
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.
Sly goose (Zool.), the common sheldrake; -- so named from
Syn: Cunning; crafty; subtile; wily. See Cunning.