We suppose that the very earliest notion of pin money was literal, just enough money with which a wife could buy pins.
This would have been an exceedingly small sum, indicated by the expression “not worth a pin,” one of the earliest in our language.
But in the early sixteenth century and onward the amount was considerably larger.
“Money to buy her pins” was enough, not only for the purchase of pins, but for all other personal expenses.
It was usually a fixed annual allowance in the olden days, and, in England, is still often provided for by the annual rentals of certain properties settled upon the wife.