Grave
Noun and な adjective
しんこく
甲状腺異常のある日本の子どもたちの数が増えているのは、深刻な問題です。
It’s a serious problem that the number of Japanese children with thyroid abnormalities have been increasing.
A deep carve is very serious and grave. Just imagine getting cut with a sword. If the carve is deep, well, that's serious.
This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own.