Sleep. In illustrations such as comics, three (or more) Z's are often used to represent sleep or snoring. I'm hoping to get some big Z's during the long layover before our next flight. It's been a hard week for Jeff—he needs some big Z's.
See also: big
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.
n. sleep. I need me some of them big Zs.
McGraw-Hill's Dictionary of American Slang and Colloquial Expressions Copyright © 2006 by The McGraw-Hill Companies, Inc. All rights reserved.