observer
Definitions
A person who watches or notices something, especially in a professional or scientific capacity.
A person who attends an event or meeting to watch and listen without participating.
A person who follows or adheres to a custom, rule, or law.
Examples
The neutral observer noted every detail of the heated debate.
As a keen observer of human nature, she often writes stories based on people she meets.
The telescope allows the observer to see distant galaxies with incredible clarity.
Synonyms
spectator witness onlooker viewer beholder watcher bystander