Spend less, be more frugal, as in Business has been bad, so we'll have to tighten our belts. This metaphoric term alludes to pulling in one's belt after losing weight from not having enough to eat. [First half of 1900s]
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.