Extravagance (noun)

1. The quality or state of being excessive or extreme; excessive expenditure of money, resources, etc.
2. A very costly or lavish thing, action, or practice.

Origin:

From latin extravagans "straying beyond", present participle of extravagari "to wander beyond bounds, to be excessive," from extra- "beyond" + vagari "to wander".

Examples:

1. The wedding was an extravagance that left the couple in debt.
2. The new car is a luxury, but buying it would be an extravagance.
3. The company's expenditures on advertising were criticized as extravagances.
4. The lavish party was seen as an extravagance by many of the guests.
5. The diamond necklace was an extravagance that she couldn't afford.