The term 'Main Line' can be broken down into three crossword solutions: AORTA (5 letters), ARTERY (6 letters), and AXIS (4 letters). AORTA is the main ARTERY of the body, carrying oxygen-rich blood from the heart to the rest of the body. ARTERY is a type of blood vessel that carries blood away from the heart. Finally, AXIS is an imaginary line that passes through the center of a body or object. All three of these terms are related to the Main Line, which is a major transportation route in the United States.