The following Q&A is excerpted from Clifford Mishler’s Coins: Questions & Answers:
Q: What is an “Eagle” as the term applies to U.S. coins?
A: A 10-dollar gold piece. Alexander Hamilton, a strong advocate of decimal denomination coinage, proposed that establishing a monetary system comprised of 100 units to a dollar and 10 dollars to an Eagle would enable the average citizen to more easily understand its mathematical structure. The term was never used on the coin itself to denote its value, but the 10-dollar gold coin has been known as an “Eagle” down through the years. The term has also been applied to the divisions and multiple of the 10-dollar gold piece: Quarter eagle for $2.50, half eagle for $5, and double eagle for $20. Gold coins minted from 1795 to 1807 did not carry an indication of value thereon, indications of value being first incorporated with introduction of the Capped Bust half eagle in mid-1807 and on the quarter eagle the following year. With the eagle not being minted from 1805 through 1837, the $10 denominational value first appeared on the eagles of 1838.