The crossword solution for the term 'Aaron Burr, ___' is 'SIR, ' which is a three letter word. Aaron Burr was an American politician who served as the third Vice President of the United States from 1801 to 1805 under President Thomas Jefferson. He is best known for his duel with Alexander Hamilton, which resulted in Hamilton's death. Burr was later tried for treason but was acquitted. He was also a lawyer and military officer.