Expense vs Undefined - What's the difference?

As a noun expense

is a spending or consuming often specifically an act of disbursing or spending funds.

is to charge a cost against an expense account; to bill something to the company for which one works.

lacking a definition or value.

(wikipedia expense) (en noun)

A spending or consuming. Often specifically an act of disbursing or spending funds.

She went to great expense to ensure her children would get the best education.

Buying the car was a big expense , but will be worth it in the long run.

We had a training weekend in New York, at the expense of our company.

* , Sonnet 44:

Husband nature's riches from expense .

That which is expended, laid out, or consumed. Sometimes with the notion of loss or damage to those on whom the expense falls.

Jones reached the final at the expense of Jones, who couldn´t beat him.

(obsolete) Loss.

* , Sonnet 30:

And moan the expense of many a vanished sight.

* (that which is expended) cost, charge, outlay, disbursement, expenditure, payment

* expense account

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.

* expense magazine, (Military):'' a small magazine containing ammunition for immediate use. - Henry Lee Scot ''Military Dictionary ----

(wikipedia undefined) (-)

Lacking a definition or value.

(mathematics, computing) That does not have a meaning and is thus not assigned an interpretation.

The result of division by zero is undefined .

* defined