on the sly
 偷偷地,祕密地,暗地里


 Sly a. [Compar. Slier or Slyer; superl. Sliest or Slyest.]
 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 Zool., the common sheldrake; -- so named from its craftiness.
 Syn: -- Cunning; crafty; subtile; wily. See Cunning.


 on the sly
      adv : in a furtive manner; "the soldiers were furtively crawling
            through the night" [syn: furtively]