lightyear silentbob light-year also light year (ltyîr) n. The distance that light travels in a vacuum in one year, approximately 9.46 trillion (9.46 × 1012) kilometers or 5.88 trillion (5.88 × 1012) miles. Informal. A long way. Often used in the plural: a small town light-years away from the action of the capital. 050929 what's it to you? who go blather from