1. occurring or found infrequently; markedly uncommon: a rare disease. 2. having the component parts loosely compacted; thin: rare gases. 3. unusually great. 4. admirable; exemplary: She showed rare tact in inviting them.
Rare-earths are to be distinguished from critical minerals, which are materials of strategic or economic importance that are defined differently by different countries, [b] and rare-earth minerals, which are minerals that contain one or more rare-earth elements as major metal constituents.