As a teenager she would 'sneak' out (of her house/apartment) at night to visit her boyfriend.
I'm going to 'sneak' a smoke. [=I'm going to smoke a cigarette while nobody is watching]
She took a 'sneak peek' [=a secret look] at the birthday presents hidden in the closet.
(..) by not protecting Gongmen City? - If we all fight together... - Then the weapon would kill everyone. Oh, would it? Then we use... a sneak attack! - We get inside and then... - And then you will be stopped... ...by the unstoppable weapon. Nothing's unstoppable except for me when I'm stopping you (..)2011 Kung Fu Panda 2