Observer

Webster's Dictionary of the English Language

·noun A sycophantic follower.

II. Observer ·noun One who fulfills or performs; as, an observer of his promises.

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

IV. Observer ·noun 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.