observer

observer is a Noun

Definition:

[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. Shak. Careful observers may foretell the hour, By sure prognostic, when to dread a shower. Swift.

[2] One who keeps any law, custom, regulation, rite, etc.; one who conforms to anything in practice. "Diligent observers of old customs." Spenser. These... hearkend unto observers of times. Deut. xviii. 14.

[3] One who fulfills or performs; as, an observer of his promises.

[4] A sycophantic follower. [Obs.] Beau. & Fl.