To reduce, restrict, or limit one's budget or expenses; to live more modestly or make financial sacrifices. (Alluding to having a thinner waist line due to having less to eat.) It's pretty galling to see the CEO driving up to work in a brand new company car while the rest of us are being told to take in our belts to help save the business. With your mother out of work, we're all going to have to take in our belts a notch or two for a little while. I really love my new job, but it pays a lot less so I've had to start taking in my belt a notch.