It's just the adverbial form of sneak or sneaky. It's not a real word and it damned well should be!
I went into Dr. Aweful's mountain lab sneakily, and stole his blueprints for a flying monkey machine!
by Felix January 09, 2005
Can you define these popular missing words?
I followed bob sneakily around the building and scaried him.
by Blackmoondust November 13, 2009