sly : Idioms & Phrases
By the sly , ∨ On the sly
- in a sly or secret manner. Colloq. "Gazed on Hetty's charms by the sly." G. Eliot.
Webster 1913
on the sly
-
adverb in a furtive manner
furtively.
- the soldiers were furtively crawling through the night
WordNet
Sly goose
(Zoöl.) , the common sheldrake; so named from its craftiness.