S0509100 (snē′kĭng)adj.1. Acting in a stealthy, furtive way.2. Unavowed; secret.3. Gradually growing or persistent: a sneaking hunch.sneak′ing·ly adv.Thesaurus
Adv.
1.
sneakingly - in a sneaky manner; "I always felt sneakingly that I wanted to be a concert pianist"