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Webster 1913 Edition

Noun.

The quality or state of being sly.

, SLYNESS. [See Slily, Sliness.]

slyness ‎(countable and uncountable, plural slynesses)

(uncountable) The state or quality of being being sly.
With his natural slyness, he was able to talk his way out of trouble.
(countable) The result or product of being sly.

quality of being sly