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[slahy] /slaɪ/
adjective, slyer or slier, slyest or sliest.
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
1150-1200; Middle English sly, sley < Old Norse slœgr sly, cunning
Related forms
slyly, slily, adverb
slyness, noun
unsly, adjective, unslyer or unslier, unslyest or unsliest.
unslyly, unslily, adverb
unslyness, noun
1. artful, subtle, foxy, crafty, shrewd, astute. 2. surreptitious, furtive, underhand, clandestine.
1. direct, obvious. Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2015.
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Examples from the Web for sly
Contemporary Examples
Historical Examples
  • The Master had a brother who used to preach to the Negroes on the sly.

  • The sly, wicked Mimi came slinking to the place where the dragon lay.

  • "Perhaps he intended that to be the play," said Mrs. Charlston, with a sly wink looking to Fred.

    The Black-Sealed Letter Andrew Learmont Spedon
  • All the sly blabbing, all the vague chatter of sacristies resounded in his ears.

  • "She is sly, that old woman," he remarked, when his mother explained to him why breakfast was late.

    The Two Brothers Honore de Balzac
British Dictionary definitions for sly


adjective slyer, slyest, slier, sliest
crafty; artful: a sly dodge
insidious; furtive: a sly manner
playfully mischievous; roguish: sly humour
on the sly, in a secretive manner
Derived Forms
slyly, slily, adverb
slyness, 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
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Word Origin and History for 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."

Online Etymology Dictionary, © 2010 Douglas Harper
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Idioms and Phrases with sly


see: on the sly
The American Heritage® Idioms Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
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