Greenback (noun)

1. A U.S. paper dollar, especially one issued during and after the Civil War.
2. A slang term used to refer to the US dollar in general.

Origin:

from the color of the ink on the back of paper money issued by the us government in the late 19th century.

Examples:

1. He tried to earn some greenbacks by working overtime.
2. The store only accepts greenbacks, no credit cards.
3. During the Civil War, the US government issued paper money known as greenbacks to finance the war effort.
4. In the late 19th century, the US government issued paper money with green ink on the back, thus the term greenback came into use.
5. The term greenback is also used to refer to the US dollar in general, regardless of the color of the ink on the paper money.