Observer - (Webster's 1828 Dictionary)
OBSERV'ER, n. s as z.
1. One who observes; one that takes notice; particularly, one who looks to with care, attention or vigilance.
Careful observers may foretell the hour, by sure prognostic, when to dread a shower.
Creditors are great observers of set days and times.
2. A beholder; a looker on; a spectator.
3. One who keeps any law, custom, regulation or rite; one who adheres to any thing in practice; one who performs; as a great observer of forms; an observer of old customs.
4. One who fulfills or performs; as, he is a strict observer of his word or promise.
5. One who keeps religiously; as an observer of the sabbath.