深感遗憾 is a formal, written verb phrase meaning 'to deeply regret' or 'to feel profound regret'. It combines four characters: 深 (shēn) meaning 'deep', 感 (gǎn) meaning 'to feel', 遗 (yí) meaning 'left behind' or 'lost', and 憾 (hàn) meaning 'regret' or 'sorrow'. Together, they convey an intense, sincere sense of remorse — stronger than just 遗憾 ('regret') alone. The phrase emphasizes emotional depth and gravity, often implying responsibility, loss, or missed opportunity.

This expression is commonly used in official announcements, apology letters, news reports, or diplomatic contexts — for example, when expressing sorrow over someone’s death, a policy failure, or an unavoidable cancellation. It rarely appears in casual speech; native speakers typically use simpler alternatives like 很遗憾 or 真可惜 in everyday conversation. Its tone is respectful, somber, and empathetic, making it especially appropriate when addressing serious or sensitive matters.