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See more synonyms for sly on Thesaurus.com
adjective, sly·er, sly·est.
  1. cunning or wily: sly as a fox.
  2. stealthy, insidious, or secret.
  3. playfully artful, mischievous, or roguish: sly humor.
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  1. on the sly, secretly; furtively: a tryst on the sly.
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Origin of sly

1150–1200; Middle English sly, sley, from Old Norse slœgr “sly, cunning” (originally “able to strike, able to slay”); see slay
Related formssly·ly, adverbsly·ness, nounun·sly, adjective, un·sly·er, un·sly·est.un·sly·ly, adverbun·sly·ness, noun


See more synonyms for sly on Thesaurus.com
1. artful, subtle, foxy, crafty, shrewd, astute. 2. surreptitious, furtive, underhand, clandestine.


1. direct, obvious.
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

Examples from the Web for slyness

Historical Examples

  • We shall learn if slyness and treachery are to be defeated by fair-going and honour.

    The O'Ruddy

    Stephen Crane

  • It was like a child, frightened into slyness, coaxing its mother.

    Little Novels of Italy

    Maurice Henry Hewlett

  • He combines the ferocity of the tiger, the slyness of the fox, and the shape of a monkey.

    The Kentucky Ranger

    Edward T. Curnick

  • She had read him and was openly rejoicing in what she thought his slyness.

    The Call of the Blood

    Robert Smythe Hichens

  • Now, however, the diabolical reason of his slyness was apparent.

    The heart of happy hollow

    Paul Laurence Dunbar

British Dictionary definitions for slyness


adjective slyer, slyest, slier or sliest
  1. crafty; artfula sly dodge
  2. insidious; furtivea sly manner
  3. playfully mischievous; roguishsly humour
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  1. on the sly in a secretive manner
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Derived Formsslyly or slily, adverbslyness, noun

Word Origin

C12: from Old Norse slǣgr clever, literally: able to strike, from slā to slay
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

Word Origin and History for slyness


mid-14c., from sly (adj.) + -ness.

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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."

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Online Etymology Dictionary, © 2010 Douglas Harper

Idioms and Phrases with slyness


see on the sly.

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The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.