"Webster’ American Dictionary of the English Language, published by G&C Merriam Co. in 1864, was the first to formally define inflation as an economic term:
undue expansion or increase, from over-issue; — said of currency."
https://www.clevelandfed.org/en/newsroom-and-events/publicat...
"its original meaning—a rise in the general price level caused by an imbalance between the quantity of money and trade needs"