Source : Webster's Revised Unabridged Dictionary (1913)

Lookout \Look"out`\, n.
   1. A careful looking or watching for any object or event.

   2. The place from which such observation is made.

   3. A person engaged in watching.

   4. Object or duty of forethought and care; responsibility.
      [Colloq.]

Source : WordNet®

lookout
     n 1: a person employed to watch for something to happen [syn: {lookout
          man}, {sentinel}, {sentry}, {watch}, {spotter}, {scout},
           {picket}]
     2: an elevated post affording a wide view [syn: {observation
        post}]
     3: a structure commanding a wide view of its surroundings [syn:
         {observation tower}, {lookout station}, {observatory}]
     4: the act of looking out [syn: {outlook}]