Definition: a penalty such as a fine; to take (something) from another person by means of unseemly or deceptive methods.
Why I Looked It Up
Found in a book about the oil industry:
Domestic creditors had already been mulcted by inflation.
The implication is that inflation “stole” value from the people who were owed money (the absolute dollars in which they would be repaid would be worth less because of inflation).