January 10, 1772:

“Believe me sir I dun as hard as is proper.” This sentence always kind of stood out to me. When read with a modern ear, one hears, “I done as hard as is proper,” and it makes him sound uneducated. But, this is Hamilton, and I don’t think he would have written such a poorly formed sentence, even at 14.

So I searched the archives for other times he might have used the word or spelling “dun.” I found none others, except for a footnote referencing a letter from his old friend Robert Troup, in 1802, to another mutual close friend, Rufus King: “Hamilton is closely pursuing the law, and I have at length succeeded in making him somewhat mercenary. I have known him latterly to dun his clients for money, and in settling an account with me the other day, he reminded me that I had received a fee for him in settling a question referred to him and me jointly.”

So then I consulted the etymology:

dun “to insist on payment of debt,” 1620s

It means “to invoice.” Of course. I also love this particular letter (the whole of which can be read here), because Hamilton, who was a day away from turning fifteen, thanks his employer for the gift of apples, which presumably had great significance for an impoverished clerk of his low station. Also he alludes to Captain Newton and his cargo of mules, which as other nerds like me will know, turns into a total debacle about three weeks later.