rare (Adjective) — Not widely known; especially valued for its uncommonness. ex. "a rare word" ex. "rare books"
rare (Adjective) — Recurring only at long intervals. ex. "a rare appearance" ex. "total eclipses are rare events"
rare (Adjective) — Not widely distributed. ex. "rare herbs" ex. "rare patches of green in the desert"
rare (Adjective) — Having low density. ex. "rare gasses"
rare (Adjective) — Marked by an uncommon quality; especially superlative or extreme of its kind. ex. "what is so rare as a day in June" ex. "a rare skill"
rare (Adjective) — (of meat) cooked a short time; still red inside. ex. "rare roast beef"