The Dollar, Money or Debt Instrument?

If you look at the top of the dollar, you will see "Federal Reserve Note". A note is a debt instrument, a legal document that binds a party to repay debt within an agreed period, with specified terms. So why is our "money" labeled a note?

The Federal Reserve Bank is a private corporation and they issue these notes to the U.S. Treasury, the treasury endorses it and it is backed by the Corporation of the United States' ability to tax the shit out of its citizens.

Our money is a debt instrument. If that spurred some interest, go dig, there's a lot to this.