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.
(..) He took it! He took it. I seen him. He's always stuffing his face when master's not looking. That's a filthy lie! You stinking, two-faced sneak! - Sam! Call me... Stop it! Sam! - Sam! No! (..)2003 The Lord of the Rings: The Return of the King
(..) Sneaking? Sneaking? Fat Hobbit is always so polite. Sméagol shows them secret ways that nobody else could find... ...and they say "sneak." Sneak? Very nice friend. Oh, yes, my precious. - Very nice, very nice. - All right. All right! (..)2003 The Lord of the Rings: The Return of the King