› [C, U] the money that you spend on something: You have to pay your own medical expenses. He eventually found her the car she wanted, at great expense (= it cost him a lot of money).
at the expense of sth › If you do one thing at the expense of another, doing the first thing harms the second thing: He spent a lot of time at work, at the expense of his marriage.
at sb's expense › If you do something at someone's expense, they pay for it: We went on holiday at my father's expense. › in order to make someone look stupid: Stop making jokes at my expense.