The Collaborative International Dictionary of English v.0.48:

Stealthy \Stealth"y\ (-[y^]), a. [Compar. Stealthier
   (-[i^]*[~e]r); superl. Stealthiest.]
   Done by stealth; accomplished clandestinely; unperceived;
   secret; furtive; sly.
   [1913 Webster]

         [Withered murder] with his stealthy pace, . . .
         Moves like a ghost.                      --Shak.
   [1913 Webster]

WordNet (r) 3.0 (2006):

stealthy
    adj 1: marked by quiet and caution and secrecy; taking pains to
           avoid being observed; "a furtive manner"; "a sneak
           attack"; "stealthy footsteps"; "a surreptitious glance at
           his watch" [syn: furtive, sneak(a), sneaky,
           stealthy, surreptitious]

Moby Thesaurus II by Grady Ward, 1.0:

96 Moby Thesaurus words for "stealthy":
   Machiavellian, Machiavellic, acute, arch, artful, astute,
   back-door, backstairs, cagey, canny, catlike, catty, clandestine,
   clever, closet, covert, crafty, cunning, cute, deceitful, deep,
   deep-laid, designing, diplomatic, doggo, feline, foxy, furtive,
   guileful, hidden out, hidlings, hole-and-corner, hugger-mugger,
   hush-hush, in ambush, in hiding, in the wings, ingenious,
   insidious, inventive, knowing, lurking, noiseless, on tiptoe,
   pawky, politic, privy, prowling, pussyfoot, pussyfooted, quiet,
   ready, resourceful, scheming, secret, secretive, serpentine, sharp,
   shifty, shrewd, silent, skulking, slick, slinking, slinky,
   slippery, sly, smooth, snaky, sneak, sneaking, sneaky, sophistical,
   stealing, stealthful, strategic, subtile, subtle, supple,
   surreptitious, tactical, trickish, tricksy, tricky, under cover,
   under-the-counter, under-the-table, undercover, underground,
   underhand, underhanded, unobtrusive, vulpine, waiting concealed,
   wary, wily