Source : Webster's Revised Unabridged Dictionary (1913)

Sneak \Sneak\ (sn[=e]k), v. i. [imp. & p. p. {Sneaked}
   (sn[=e]kt); p. pr. & vb. n. {Sneaking}.] [OE. sniken, AS.
   sn[=i]can to creep; akin to Dan. snige sig; cf. Icel.
   sn[=i]kja to hanker after.]
   1. To creep or steal (away or about) privately; to come or go
      meanly, as a person afraid or ashamed to be seen; as, to
      sneak away from company.

Sneaking \Sneak"ing\, a.
   Marked by cowardly concealment; deficient in openness and
   courage; underhand; mean; crouching. -- {Sneak"ing*ly}, adv.
   -- {Sneak"ing*ness}, n.

Source : WordNet®

sneaking
     adj : not openly expressed; "a sneaking suspicion" [syn: {sneaking(a)},
            {unavowed}]