let slip by
let (someone or something) slip by
1. To allow someone or something to quickly pass by one. Don't let anyone slip by. We don't want the scene of the crime to be contaminated before the detectives have a chance to look things over. Their goalkeeper is not in his usual form today—that's the fourth goal he's let slip by already!
2. To fail to detect someone or something. She has an eagle eye for mistakes—she hasn't let a single error slip by since she started proofreading for us. The inattentive security guard kept letting prisoners slip by into the storage room where contraband was stored.
3. To fail to remember or pay attention to something that one had planned or scheduled. I can't believe you let our meeting slip by—we've had that planned out for over a month! She lets everything else in his life slip by when she gets so focused on a project like this.
4. To allow a period of time to pass or be spent idly or without notice. I don't want to let the whole summer slip by without going anywhere nice for a vacation. Sorry, I got distracted playing my game and ended up letting the afternoon slip by.
5. To fail to capitalize on some opportunity. What are you waiting for, call them back! Don't let such an amazing chance slip by!
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.
let something slip byand let something slide by
1. Lit to permit something to move quickly by oneself. He let the ball slip by and he knew he had better get the next one. The careless cashier let the leaky milk carton slide by.
2. Fig. to forget or miss an important time or date. I'm sorry I just let your birthday slip by. I let it slide by accidentally.
3. Fig. to waste a period of time. You wasted the whole day by letting it slip by. We were having fun, and we let the time slide by.
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs. © 2002 by The McGraw-Hill Companies, Inc.