rare
Not happening or found often; very uncommon.
Something that is rare is hard to find because there aren't many of them. A rare baseball card might be valuable because only a few were printed. A rare disease affects very few people. When a museum displays a rare artifact, it means similar objects almost never survive from that period in history.
Rare things become precious partly because of their scarcity. Gold is rare compared to iron, which is one reason it costs so much more. Four-leaf clovers are rare mutations that appear in only about one in 5,000 clover plants, making them prized good-luck symbols. Scientists get excited when they discover a rare species because finding it is so unlikely.
The word also describes something that doesn't happen often. A solar eclipse is a rare event you might see only a few times in your life. Getting a perfect score might be rare for most students but common for someone who always studies hard.
In cooking, rare means meat that's been cooked only briefly, leaving the inside red and cool. A rare steak spends just a short time on the heat.
The opposite of rare is common or abundant. Something rarely happens when it occurs infrequently, like “She rarely forgets her homework.”