noun
kanji 'big shell' radical
Refers to the kanji radical 頁 (おおがい), literally 'big shell', which appears in characters related to the head or pages.
「頁」は部首の一つで、大貝と呼ばれる。
'頁' is one of the radicals, called 大貝.
The reading おおがい comes from the kanji components 大 (big) and 貝 (shell), describing the shape of the radical 頁.