observer

noun7

1. •
   One who makes observations, monitors or takes notice.

   • Most impartial observers agreed that Sampras had not served well.
2. •
   A crew member on an aircraft who makes observations of enemy positions or aircraft.

   • The only crew-member to survive the crash was the Canadian observer.
3. •
   A sentry etc. manning an observation post.

   • We waited till dusk when the observers' vision was poorest.
4. •
   Synonym of spotter.
5. •
   A person sent as a representative, to a meeting or other function to monitor but not to participate.

   • The UN sent many observers to the country's first elections.
6. •
   A country or other entity which has limited participation rights within an organization.

   • The Vatican and Palestine have observer status at the UN.
7. •
   One who adheres or follows laws, guidelines, etc.

   • I shall be an observer of the local customs.