duty
 
a committment
an obligation
moral obligation
legal obligation
a service in the armed forces
Civic Duty
a duty to your country



example
Girl Scout Promise

I promise to do my duty to God and my country,
to help other people at all times
and to obey the Girl Scout Laws.

http://www.thefreedictionary.com/duty

http://en.wikipedia.org/wiki/Duty

http://www.merriam-webster.com/dictionary/duty

 a tax
There was a duty tax on the item brought in the country.