Source : Webster's Revised Unabridged Dictionary (1913)

Stealthiness \Stealth"i*ness\, n.
   The state, quality, or character of being stealthy; stealth.

Source : WordNet®

stealthiness
     n : a disposition to be sly and stealthy and to do things
         surreptitiously [syn: {furtiveness}, {sneakiness}]