na-adjective
A rare, literary adjectival noun meaning something is uncommon or extraordinary. Not used in everyday conversation; more common synonyms like 珍しい or まれ are preferred.
この標本は珍稀なものだ。
This specimen is a rare one.
彼の才能は珍稀である。
His talent is unusual.
The kanji 珍 (rare, precious) and 稀 (rare, uncommon) combine to reinforce the meaning of rarity. The exact historical derivation is uncertain; it is a Sino-Japanese compound (kango).