Webster's Revised Unabridged Dictionary -- Volume DE

1. That which is due; payment. [Obs. as signifying a material thing.]

When thou receivest money for thy labor or ware, thou receivest thy duty.
Tyndale.

2. That which a person is bound by moral obligation to do, or refrain from doing; that which one ought to do; service morally obligatory.

Forgetting his duty toward God, his sovereign lord, and his country.
Hallam.

3. Hence, any assigned service or business; as, the duties of a policeman, or a soldier; to be on duty.

With records sweet of duties done.
Keble.

To employ him on the hardest and most imperative duty.
Hallam.

Duty is a graver term than obligation. A duty hardly exists to do trivial things; but there may be an obligation to do them.
C. J. Smith.

4. Specifically, obedience or submission due to parents and superiors. Shak.

5. Respect; reverence; regard; act of respect; homage. "My duty to you." Shak.

6. (Engin.) The efficiency of an engine, especially a steam pumping engine, as measured by work done by a certain quantity of fuel; usually, the number of pounds of water lifted one foot by one bushel of coal (94 lbs. old standard), or by 1 cwt. (112 lbs., England, or 100 lbs., United States).

7. (Com.) Tax, toll, impost, or customs; excise; any sum of money required by government to be paid on the importation, exportation, or consumption of goods.

An impost on land or other real estate, and on the stock of farmers, is not called a duty, but a direct tax. [U.S.]

-- Ad valorem duty, a duty which is graded according to the cost, or market value, of the article taxed. See Ad valorem.