• 深海しんかい — deep sea
• 深夜しんや — late at night
• 深刻しんこく — serious / grave
• 深呼吸しんこきゅう — deep breath
• 深度しんど — depth (measurement)

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深 is a 形声 character. The radical 氵(さんずい) means water, while the right part serves as the phonetic for シン. Originally, it described water sinking or flowing into depth. Over time, it broadened to mean deepness in both physical and metaphorical senses.

この湖みずうみは 非常ひじょうに 深ふかい。
This lake is extremely deep.

理解りかいを 深ふかめるために 説明せつめいが 必要ひつようです。
Further explanation is needed to deepen understanding.