This is the 2703rd most frequent Korean word.
심해
"심해" means "deep sea" in English.
In this sentence, '심해지다' is again used as a verb, meaning 'to worsen'.
그의 병이 심해지기 전에 치료를 받아야 합니다.
He needs to receive treatment before his illness worsens.
In this sentence, '심해' is used as a noun referring to the deep sea.
심해는 깊고 어두운 바다의 일부입니다.
The deep sea is a part of the ocean that is deep and dark.
Here, '심해' is part of the verb '심해지다', which means 'to become severe'.