From BiblePortal Wikipedia

Webster's Dictionary [1]

(1): ( superl.) Nearly raw; partially cooked; not thoroughly cooked; underdone; as, rare beef or mutton.

(2): ( a.) Early.

(3): ( superl.) Not frequent; seldom met with or occurring; unusual; as, a rare event.

(4): ( superl.) Of an uncommon nature; unusually excellent; valuable to a degree seldom found.

(5): ( superl.) Thinly scattered; dispersed.

(6): ( superl.) Characterized by wide separation of parts; of loose texture; not thick or dense; thin; as, a rare atmosphere at high elevations.

King James Dictionary [2]

Rare, a. L. rarus, thin.

1. Uncommon not frequent as a rare event a rare phenomenon. 2. Unusually excellent valuable to a degree seldom found.

Rare work, all fill'd with terror and delight.

Above the rest I judge one beauty rare.

3. Thinly scattered. 4. Thin porous not dense as a rare and attenuate substance.

Water is nineteen times lighter and by consequence nineteen times rarer than gold.

5. Nearly raw imperfectly roasted or boiled as rare beef or mutton eggs roasted rare.