1.Definition: (of meat) cooked a short time; still red inside
"Rare roast beef"
2.Definition: having low density
"Rare gasses", "Lightheaded from the rarefied mountain air"
3.Definition: marked by an uncommon quality; especially superlative or extreme of its kind
"What is so rare as a day in June", "A rare skill"
4.Definition: not widely distributed
"Rare herbs", "Rare patches of green in the desert"
5.Definition: not widely known; especially valued for its uncommonness
"A rare word", "Rare books"
6.Definition: recurring only at long intervals
"A rare appearance", "Total eclipses are rare events"