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Synonyms

sly

American  
[slahy] / slaɪ /

adjective

slyer, comparative slier, comparative slyest, superlative sliest superlative
  1. cunning or wily.

    sly as a fox.

    Synonyms:
    astute, shrewd, crafty, foxy, subtle, artful
    Antonyms:
    obvious, direct
  2. stealthy, insidious, or secret.

    Synonyms:
    clandestine, underhand, furtive, surreptitious
  3. playfully artful, mischievous, or roguish.

    sly humor.


idioms

  1. on the sly, secretly;

    a tryst on the sly.

sly British  
/ slaɪ /

adjective

  1. crafty; artful

    a sly dodge

  2. insidious; furtive

    a sly manner

  3. playfully mischievous; roguish

    sly humour

"Collins English Dictionary — Complete & Unabridged" 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

noun

  1. in a secretive manner

"Collins English Dictionary — Complete & Unabridged" 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
sly More Idioms  
  1. see on the sly.


Other Word Forms

Derived Forms

Etymology

Origin of sly

First recorded in 1150–1200; Middle English sly, sley , from Old Norse slœgr “sly, cunning” (originally “able to strike, able to slay”); see slay ( def. )

Explanation

When you're sly, you're crafty, cunning, tricky, and wily. Being sly is being deceitful, though not in the worst way. If you're good at lying, you're quite sly: people who are sly are good at pulling one over on other people. Being sly helps you get away with things. If you made a mess in your house but got your parents to blame the dog, that was sly. Being sly means you're not being honest, but this word has kind of a harmless flavor to it. Someone who killed someone and lied about it would not be described as sly. Slyness has to do with smaller, sneakier, more harmless kinds of lying.

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Vocabulary lists containing sly

Example Sentences

Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.

You have to be clever, not sly, in how you deal with it.

From BBC • May 8, 2026

I saw his pale skin turned purple, his sly mouth gone flat.

From Slate • Apr. 23, 2026

She has a sly way of imparting lessons, often with playfulness.

From Los Angeles Times • Jan. 14, 2026

Here, it is a man whose labor disappears behind a woman’s byline, a sly inversion of the far more familiar historical pattern.

From Salon • Dec. 25, 2025

“I’ll try, but it was a very ungentlemanly thing to do, I didn’t think you could be so sly and malicious, Laurie,” replied Meg, trying to hide her maidenly confusion under a gravely reproachful air.

From "Little Women" by Louisa May Alcott

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