A spending or consuming, often a disbursement of funds.
Buying the car was a big expense, but will be worth it in the long run.
The elimination or consumption of something, sometimes with the notion of loss or damage to the thing eliminated.
Jones reached the final at the expense of Smith, who couldn't beat him.
Loss.
To charge a cost against an expense account; to bill something to the company for which one works.
It should be acceptable to expense a business lunch with a client.