expression, noun-modifying (irregular)
Used prenominally to describe something exceptionally uncommon or remarkable. Often modifies nouns like 才能, 光景, or 出来事.
彼は稀に見る才能の持ち主だ。
He has a rare talent.
昨夜は稀に見る美しい星空だった。
Last night we had an extraordinarily beautiful starry sky.
珍しい is a general adjective meaning 'unusual' or 'rare', while 稀に見る is a set phrase used prenominally to emphasize exceptional rarity or remarkableness.
From 稀 (まれ, 'rare') + に (adverbial particle) + 見る (みる, 'to see'), literally 'seen rarely'.