- cunning or wily: sly as a fox.
- stealthy, insidious, or secret.
- playfully artful, mischievous, or roguish: sly humor.
- on the sly, secretly; furtively: a tryst on the sly.
Origin of sly
SynonymsSee more synonyms for sly on Thesaurus.com
- crafty; artfula sly dodge
- insidious; furtivea sly manner
- playfully mischievous; roguishsly humour
- on the sly in a secretive manner
Word Origin and History for on the sly
c.1200, "skillful, clever, dexterous," from Old Norse sloegr "cunning, crafty, sly," from Proto-Germanic *slogis (cf. Low German slu "cunning, sly," German schlau), probably from base *slak- "to strike, hit" (see slay (v.)), with an original notion of "able to hit." Cf. German verschlagen "cunning, crafty, sly," schlagfertig "quick-witted," literally "strike-ready," from schlagen "to strike." A non-pejorative use of the word lingered in northern English dialect until 20c. On the sly "in secret" is recorded from 1812. Sly-boots "a seeming Silly, but subtil Fellow" is in the 1700 "Dictionary of the Canting Crew."
Idioms and Phrases with on the sly
on the sly
Furtively, secretly, as in She's always eating cookies on the sly. The adjective sly, which means “cunning” or “crafty,” is here used as a noun. [c. 1800]
see on the sly.