adjective \ ˈslī \
|Updated on: 12 Aug 2018

Definition of sly

slyer also slier play \ˈslī(-ə)r\; slyest also sliest play \ˈslī-əst\
1 chiefly dialectal
a : wise in practical affairs
b : displaying cleverness : ingenious
2 a : clever in concealing one's aims or ends : furtive
b : lacking in straightforwardness and candor : dissembling
3 : lightly mischievous : roguish
  • a sly jest


or less commonly slily adverb


on the sly
: in a manner intended to avoid notice

Examples of sly in a Sentence

  1. the movie pairs a sly, dissembling ex-con with an upstanding, straight-arrow cop

  2. why, you sly fellow! I had no idea you were planning my birthday party

Recent Examples of sly from the Web

These example sentences are selected automatically from various online news sources to reflect current usage of the word 'sly.' Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.

Origin and Etymology of sly

Middle English sleighe, sli, from Old Norse slœgr; akin to Old English slēan to strike — more at slay

Synonym Discussion of sly

sly, cunning, crafty, wily, tricky, foxy, artful, slick mean attaining or seeking to attain one's ends by guileful or devious means. sly implies furtiveness, lack of candor, and skill in concealing one's aims and methods.
    • a sly corporate raider
cunning suggests the inventive use of sometimes limited intelligence in overreaching or circumventing.
    • the cunning fox avoided the trap
crafty implies cleverness and subtlety of method.
    • a crafty lefthander
wily implies skill and deception in maneuvering.
    • the wily fugitive escaped the posse
tricky is more likely to suggest shiftiness and unreliability than skill in deception and maneuvering.
    • a tricky political operative
foxy implies a shrewd and wary craftiness usually involving devious dealing.
    • a foxy publicity man planting stories
artful implies indirectness in dealing and often connotes sophistication or cleverness.
    • elicited the information by artful questioning
slick emphasizes smoothness and guile.
    • slick operators selling time-sharing

SLY Defined for English Language Learners


Definition of sly for English Language Learners

  • : clever in a dishonest way

  • : showing that you know a secret

SLY Defined for Kids


adjective \ ˈslī \

Definition of sly for Students

slier or slyer; sliest or slyest
1 : both clever and tricky
2 : tending to keep secrets and hide intentions
3 : mischievous 2
  • There were teachers all over the place, and any kind of fighting or taunting, above a sly pinch … was out.
  • —Lynne Reid Banks, The Indian in the Cupboard




on the sly
: so as not to be seen or caught : secretly

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having an air of easy unconcern

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