One who makes observations, monitors or takes notice
A crew member on an aircraft who makes observations of enemy positions or aircraft
A person sent as a representative, to a meeting or other function to monitor but not to participate
One who adheres or follows laws, guidelines, etc.
A country or other entity which has limited participation rights within an organization.
A sentry etc. manning an observation post
A person who writes reviews for a newspaper or other publication; a critic.
An inspector.