Definition of Stealthiness

Babylon English Dictionary
furtiveness, slyness, sneakiness, secrecy
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Stealthiness Definition from Language, Idioms & Slang Dictionaries & Glossaries
Webster's Revised Unabridged Dictionary (1913)
(n.)
The state, quality, or character of being stealthy; stealth.
  
Webster's Revised Unabridged Dictionary (1913), edited by Noah Porter. About
WordNet 2.0

Noun
1. a disposition to be sly and stealthy and to do things surreptitiously
(synonym) furtiveness, sneakiness
(hypernym) closeness, secretiveness