Belt : noun Band used to tighten the waist, to adjust the clothes to the size.
Put on, tighten your belt a notch; to tighten up a notch; take your belt a step further: not to eat, to fast to deprive yourself of food; do without something.
Make a belt: not to eat, to be deprived of meals.
Belt give it a full belt: Eat well, to satiety.
The expression "tighten your belt": Go without food - Do without something.
The date of appearance of this expression does not seem really known. However, the word belt has existed since the XNUMXth century with the meaning of "band of flexible material worn at the waist to hold a garment or as an ornament". Now, to understand the origin of the metaphorical meanings of the expression is very simple: there is no doubt that going without food for a long time allows you to tighten your belt much more. From this arises the first meaning proposed, even if here, the deprivation is absolutely not voluntary, but suffered, whether because of poverty (in general) or of a situation in which no food is accessible. It is by simple extension of the initial meaning that the expression also covers the deprivation or lack of anything that one would however want or need.