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sly

[slahy] /slaɪ/
adjective, slyer or slier, slyest or sliest.
1.
cunning or wily:
sly as a fox.
2.
stealthy, insidious, or secret.
3.
playfully artful, mischievous, or roguish:
sly humor.
Idioms
4.
on the sly, secretly; furtively:
a tryst on the sly.
Origin
1150-1200
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
Synonyms
1. artful, subtle, foxy, crafty, shrewd, astute. 2. surreptitious, furtive, underhand, clandestine.
Antonyms
1. direct, obvious.
Dictionary.com Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2014.
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British Dictionary definitions for on the sly

sly

/slaɪ/
adjective slyer, slyest, slier, sliest
1.
crafty; artful: a sly dodge
2.
insidious; furtive: a sly manner
3.
playfully mischievous; roguish: sly humour
noun
4.
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 on the sly

sly

adj.

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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Slang definitions & phrases for on the sly

on the sly

adverb phrase

Secretly and deceptively: sold that equipment on the sly


The Dictionary of American Slang, Fourth Edition by Barbara Ann Kipfer, PhD. and Robert L. Chapman, Ph.D.
Copyright (C) 2007 by HarperCollins Publishers.
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Idioms and Phrases with on the sly

on the sly

Furtively, secretly, as in She's always eating cookies on the sly. The adjective sly, which means “cunning” or “crafty,” is here used as a noun. [ c. 1800 ]

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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