Question: What is the largest coin in the us?
Disambiguated questions and answers: question: What is the largest coin ever minted in the us?
What is the largest coin ever issued in the us?
answer: Half union
gold "Half Union" pattern in 1877
1877 pattern half union
octagonal $50 piece
Panama-Pacific Exposition $50 gold commemorative
Natural Questions answer: $1 ASE Bullion (from the Wikipedia article "United States Mint coin sizes")