Collins COBUILD Advanced Learner's English Dictionary - sneak up on

1. If someone sneaks up on you, they try and approach you without being seen or heard, perhaps to surprise you or do you harm. I managed to sneak up on him when you knocked on the door. = creep up PHRASAL VERB: V P P n 2. If something sneaks up on you, it happens or occurs when you are not expecting it. Sometimes our expectations sneak up on us unawares. PHRASAL VERB: V P P n