Answer:

lightyear

Answer	Crossword Clue
LIGHTYEAR	Unit of distance (not time)
LIGHTYEAR	Astronomical distance
LIGHTYEAR	Long distance

LIGHTYEAR	About nine trillion kilometers
LIGHTYEAR	Slow period for business
LIGHTYEAR	Astronomer's measure.
LIGHTYEAR	Astronomer's unit.
LIGHTYEAR	About six trillion miles
LIGHTYEAR	Easy two semesters at school?