Observer
Observer , noun
1.
One who observes, or pays attention to, anything; especially, one engaged in, or trained to habits of, close and exact observation; as, an astronomical observer.
The observed of all observers.
Careful observers may foretell the hour,
By sure prognostic, when to dread a shower.
2.
One who keeps any law, custom, regulation, rite, etc.; one who conforms to anything in practice.
Diligent observers of old customs.
These... hearkened unto observers of times.
3.
One who fulfills or performs; as, an observer of his promises.
4.
A sycophantic follower. [Obsolete] — Beau. & Fl