Webster's Revised Unabridged Dictionary · 1913

Observant

Observant , adjective

[Latin observans, -anits, present participle of observare: compare French observant. See Observe.]

1.
Taking notice; viewing or noticing attentively; watchful; carefully attentive; as, an observant spectator; observant habits.
Wandering from clime to clime observant stray'd. — Pope
2.
Submissively attentive; obediently watchful; regardful; mindful; obedient (to); -- with of, as, to be observant of rules.
We are told how observant Alexander was of his master Aristotle. — Sir K. Digby

Observant , noun

1.
One who observes forms and rules. [Obsolete] — Hooker
2.
A sycophantic servant. [Obsolete]
Silly ducking observants, That stretch their duties nicely. — Shakespeare
3.
(Roman Catholic Church) An Observantine.