The term 'Astronomical Unit' is a unit of measurement used in astronomy. It is equal to the average distance between the Earth and the Sun, which is approximately 93 million miles. The crossword solutions for this term are PARSEC (6 letters), AEON (4 letters), and YEAR (4 letters). A parsec is a unit of length used in astronomy, equal to 3.26 light-years. An AEON is an indefinite period of time, usually considered to be very long. A year is a unit of time equal to 365 days.