tighten one's belt
tighten one's belt {v. phr.}
To live on less money than usual; use less food and other things.
When father lost his job we had to tighten our belts.
Often used in the expression "tighten one's belt another notch".
When the husband lost his job, the Smiths had to do without many things, but when their savings were all spent, they had to tighten their belts another notch.
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Source: A Dictionary of American Idioms