Dear Madame L,
I've been reading some old family letters and have found references to "mills" from different states---not lumber mills or paper mills or flour mills, but some kind of coin. Can you tell me what these are?
According to Wikipedia, the "mill" or "mil" was first proposed by the Continental Congress in 1786, "being described as the "'lowest money of account, of which 1000 shall be equal to the federal dollar.'"
Nobody uses mills any more---in fact, our country may eventually follow the lead of Canada in abolishing even the penny coin.
But mill coins, made by the states so people could pay state taxes that came to fractions of pennies, were used as recently as the 1940s. Here, for example, are four mill coins enclosed in a letter from a missionary to his family back home; in this letter, the missionary asked his family to send him some mill coins from his state for him to give as souvenirs to friends in the state where he was working.
Nowadays, we don't use the term, which is why you had to ask about it. Instead, as the Wikipedia article points out, "Discount coupons, such as those for grocery items, usually include in their fine print a statement such as 'Cash value less than 1⁄10 of 1 cent.'"