| an extraordinary or unusual thing, person, or event; an exceptional example or instance. |
| a calculus or concretion found in the stomach or intestines of certain animals, esp. ruminants, formerly reputed to be an effective remedy for poison. |
only
In addition to the idioms beginning with only, also see beauty is only skin deep; have an eye (eyes only) for; if only; in name only; not the only fish in the sea; one and only