sneak up (on someone or something)
1. To approach someone or something in a sneaky, furtive manner so as not to be noticed. Don't sneak up on me like that—you frightened the life out of me! We don't want the guards to see us, so we'll need to sneak up from the back.
2. To come up on someone or some group gradually or without being noticed. I've been so busy with my work that our wedding anniversary completely snuck up on me. The deadline is sneaking up on us, and we still haven't made any substantial progress.
Farlex Dictionary of Idioms. © 2024 Farlex, Inc, all rights reserved.