Gradually over the years usury has been redefined from being an amount asked for on top of the principle amount of a loan, to just being ‘excessive interest’. This has been a slow process, happening over the last 500 years, but before that, usury had its original and true meaning which is asking for anything over and above the principal amount loaned.
It was seen as unjust earnings and four times worse than theft in legal terms. Although it is usually applied today only to money, which is not a thing in itself but a measure of value, back then it did not just apply to the loaning of money, but to the loaning of anything. You would not loan a coat to somebody and expect a pair of trousers with it to come back and the same common sense applied to the loaning of money.