WordReference Random House Learner's Dictionary of American English © 2019
sly /slaɪ/USA pronunciation   adj.,  sly•er or sli•er, sly•est or sli•est, n. 
  1. sneaky;
    cunning:The sly old fox was able to outsmart us once again.
  2. able to avoid being seen or noticed;
    stealthy:a sly move.
  3. mischievous:sly humor.

n., Idiom.
  1. on the sly, [uncountable] secretly;
    without others knowing or seeing.
sly•ly, adv.: slyly slipped the money from the drawer.
sly•ness, n. [uncountable]

WordReference Random House Unabridged Dictionary of American English © 2019
sly  (slī),USA pronunciation adj.,  sly•er  or sli•er, sly•est  or sli•est, n. 
  1. cunning or wily:sly as a fox.
  2. stealthy, insidious, or secret.
  3. playfully artful, mischievous, or roguish:sly humor.

  1. on the sly, secretly;
    furtively:a tryst on the sly.
slyly, slily, adv. 
slyness, n. 
  • Old Norse slœgr sly, cunning
  • Middle English sly, sley 1150–1200
    • 1.See corresponding entry in Unabridged artful, subtle, foxy, crafty, shrewd, astute.
    • 2.See corresponding entry in Unabridged surreptitious, furtive, underhand, clandestine.
    • 1.See corresponding entry in Unabridged direct, obvious.

Collins Concise English Dictionary © HarperCollins Publishers::

sly /slaɪ/ adj (slyer, slyest, slier, sliest)
  1. crafty; artful: a sly dodge
  2. insidious; furtive: a sly manner
  3. playfully mischievous; roguish: sly humour
  1. on the slyin a secretive manner
Etymology: 12th Century: from Old Norse slǣgr clever, literally: able to strike, from slā to slay

ˈslyly, ˈslily adv ˈslyness n

'sly' also found in these entries:

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