Wiktionary
sneak up
vb. To approach a person or animal without being seen or heard
WordNet
sneak up
v. advance stealthily or unnoticed; "Age creeps up on you" [syn: creep up]
Usage examples of "sneak up".
So alert were they to the moment that one had to become nearly invisible and completely silent to sneak up on a monk, and even then simply jumping out and shouting “.
If you hadn't managed to sneak up on me, I'd have striped you till you wailed.
A mammoth did sneak up on me while I was looking at those ogre bodies.
Sara had a strange thought-should she sneak up to her old attic room and wait for the wave?