rare
1. [ adjective ] not widely known; especially valued for its uncommonness
Examples:

"a rare word" "rare books"

Related terms: uncommon
2. [ adjective ] recurring only at long intervals
Examples:

"a rare appearance" "total eclipses are rare events"

Related terms: infrequent
3. [ adjective ] not widely distributed
Examples:

"rare herbs" "rare patches of gree in the desert"

Related terms: scarce
4. [ adjective ] marked by an uncommon quality; especially superlative or extreme of its kind
Synonyms: uncommon
Examples:

"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"

Related terms: extraordinary
5. [ adjective ] having low density
Synonyms: rarified rarefied
Examples:

"rare gasses" "lightheaded from the rarefied mountain air"

Related terms: thin
6. [ adjective ] (of meat) cooked a short time; still red inside
Examples:

"rare roast beef"

Related terms: raw