Source : Webster's Revised Unabridged Dictionary (1913)

Headlight \Head"light`\, n. (Engin.)
   A light, with a powerful reflector, placed at the head of a
   locomotive, or in front of it, to throw light on the track at
   night, or in going through a dark tunnel.

Source : WordNet®

headlight
     n : a powerful light with reflector; attached to the front of an
         automobile or locomotive [syn: {headlamp}]