Noah Webster's New International Dictionary of the English Language

1. (a.) Early.

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

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.