Emily Dickinson Lexicon

RAR'I-TY, n. [Fr. rareté; L. raritas.]

1. Uncommonness; infrequency. Far from being fond of a flower for its rarity. – Spectator.
2. A thing valued for its scarcity. I saw three rarities of different kinds, which pleased me more than any other shows in the place. – Addison.
3. Thinness; tenuity; opposed to density; as, the rarity of air. – Digby.