Observer (noun)

1. A person who watches and reports on something, especially an event or a process.
2. A person who is present at an event but does not take part in it.
3. A person who is trained to watch and record specific information, especially as part of a scientific study or experiment.

Origin:

Late middle english from latin observare, from ob- meaning toward + servare meaning to watch.

Examples:

1. The observer took detailed notes on the behavior of the animals in their natural habitat.
2. She was an impartial observer at the meeting, taking no sides.
3. The traffic observer counted the number of cars passing by the intersection.
4. As an experienced observer, he was able to make a fair assessment of the situation.
5. The observer was tasked with recording the weather conditions every hour.