- The definition of sly is someone or something that is clever in a deceitful or cunning way.
An example of something that would be described as sly is a devious secret plot to win an award.
adjectiveslier or slyer, sliest or slyest
- Dialectal skillful or clever
- skillful at trickery or deceit; crafty; wily
- showing a secretive, crafty, or wily nature; cunningly underhanded
- mischievous in a playful way; roguish
Origin of slyMiddle English sley ; from Old Norse slœgr, clever, cunning, literally , able to strike ; from base of slā and amp; Old English slean, to strike: see slay
on the sly
adjectivesli·er , sli·est also sly·er or sly·est
- Clever or cunning, especially in the practice of deceit.
- Stealthy or surreptitious: took a sly look at the letter on the table.
- Playfully mischievous: a sly laugh.
Origin of slyMiddle English sleigh, from Old Norse slœgr.
(comparative slier or slyer, superlative sliest or slyest)
From Middle English sly, sley, from Old Norse slǣgr, slœgr (“sly, cunning”, literally “capable of hitting or striking”), from Proto-Germanic *slōgiz (“lively, agile, cunning, sly, striking”), from Proto-Indo-European *slak- (“to hit, throw”). Cognate with Icelandic slægur (“crafty, sly”), Norwegian Nynorsk sløg (“sly”), German schlau (“clever, crafty”). Related to sleight, slay.