slang Someone who spends an inordinate amount of time sleeping or lounging in bed. ("Sack" is a colloquial term for "bed.") I used to be such a sack rat when I was in college, spending entire days in bed. Now that I have kids, I'm lucky if I can get eight uninterrupted hours in bed each night.
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.
n. someone who spends a lot of time in bed; someone who does not ever seem to get enough sleep. Tom is such a sack rat. He can’t seem to get enough sleep.
McGraw-Hill's Dictionary of American Slang and Colloquial Expressions Copyright © 2006 by The McGraw-Hill Companies, Inc. All rights reserved.