The crossword solution for the term 'Mount Rushmore Nickname' is 'ABE, ' which is a three-letter nickname for Abraham Lincoln, the 16th President of the United States. Mount Rushmore is a national monument located in South Dakota, featuring the faces of four former presidents of the United States: George Washington, Thomas Jefferson, Theodore Roosevelt, and Abraham Lincoln. The nickname 'ABE' is a reference to the fact that Abraham Lincoln is one of the four presidents featured on the monument.