noun. One who observes.

noun. One who is sent to observe and report on events or proceedings without directly participating in them.

noun. undefined

noun. A crew member on a military aircraft who makes observations.

noun. A member of an armed force who watches and reports from an observation post.

noun. In experimental psychology, the general term for the subject of a psychological experiment: opposed to experimenter, the general term for the person who arranges the conditions of the experiment.

noun. One who observes or takes notice; a spectator or looker-on: as, a keen observer.

noun. One who is engaged in habitual or systematic observation, as for scientific purposes; especially, one who is trained to make certain special observations with accuracy and under proper precautions: as, an astronomical observer; a corps of observers.

noun. One who observes or keeps any law, custom, regulation, or rite; one who practises, performs, or fulfils anything: as, a careful observer of the proprieties; an observer of the sabbath.

noun. One who watches with a view to serve; an obsequious attendant or admirer; hence, a toady; a sycophant.

noun. One who observes, or pays attention to, anything; especially, one engaged in, or trained to habits of, close and exact observation.

noun. One who keeps any law, custom, regulation, rite, etc.; one who conforms to anything in practice.

noun. One who fulfills or performs.

noun. A sycophantic follower.

noun. One who makes observations, monitors or takes notice

noun. One who adheres or follows laws, guidelines, etc.

noun. A person sent as a representative, to a meeting or other function to monitor but not to participate

noun. A crew member on an aircraft who makes observations of enemy positions or aircraft

noun. A sentry etc. manning an observation post

noun. a person who becomes aware (of things or events) through the senses

noun. an expert who observes and comments on something

"Typically we will pretend the observer is a person, though it could of course be a scientific apparatus as well."

observance  observant  observation  observational  observatory  

fervor  preserver  server  

adviser  critic  economist  historian  investigator  

TV-viewer  ace  air force  beholder  bird-watcher