a small group of indispensable persons or things; "five periodicals make up the core of their publishing program"
どうしても欠かせない人や物の小グループ
nucleus
(astronomy) the center of the head of a comet; consists of small solid particles of ice and frozen gas that vaporizes on approaching the sun to form the coma and tail
彗星頭部の中心
nucleus
any histologically identifiable mass of neural cell bodies in the brain or spinal cord