The adj rare has 6 senses (first 4 from tagged texts)
1. (6) rare -- (not widely known; especially valued for its uncommonness; "a rare word"; "rare books")
2. (2) rare -- (recurring only at long intervals; "a rare appearance"; "total eclipses are rare events")
3. (2) rare -- (not widely distributed; "rare herbs"; "rare patches of green in the desert")
4. (1) rare, uncommon -- (marked by an uncommon quality; especially superlative or extreme of its kind; "what is so rare as a day in June"-J.R.Lowell; "a rare skill"; "an uncommon sense of humor"; "she was kind to an uncommon degree")
5. rare, rarefied, rarified -- (having low density; "rare gasses"; "lightheaded from the rarefied mountain air")
6. rare -- ((of meat) cooked a short time; still red inside; "rare roast beef")