What's the difference between only and owly?

Only

Definition:

(a.) One alone; single; as, the only man present; his only occupation.
(a.) Alone in its class; by itself; not associated with others of the same class or kind; as, an only child.
(a.) Hence, figuratively: Alone, by reason of superiority; preeminent; chief.
(a.) In one manner or degree; for one purpose alone; simply; merely; barely.
(a.) So and no otherwise; no other than; exclusively; solely; wholly.
(a.) Singly; without more; as, only-begotten.
(a.) Above all others; particularly.
(conj.) Save or except (that); -- an adversative used elliptically with or without that, and properly introducing a single fact or consideration.