The Collaborative International Dictionary
Sneaking \Sneak"ing\, a. Marked by cowardly concealment; deficient in openness and courage; underhand; mean; crouching. -- Sneak"ing*ly, adv. -- Sneak"ing*ness, n.
Wiktionary
adv. In the manner of one who is sneaking or sneaky; slyly, covertly.
WordNet
adv. in a sneaky manner; "I always felt sneakingly that I wanted to be a concert pianist"
Usage examples of "sneakingly".
Collaci might have been sneakingly grateful for my pacifist powwow with the Sirocco Brothers, but his hired guns appeared to lack the imagination.
He looked at his companion sneakingly, he looked at him admiringly, he looked at him boldly, and put up one leg on the sofa.
If he who struck him, though he did so sneakingly and treacherously, had drawn his sword and stood and faced him, then he who had been struck would have received offence and insult at the same time.