be sad
悵 centers on a lingering sadness or disappointment, a feeling of being let down or regretful.
悵 combines the heart radical 忄 with 長, which likely contributes the sound. The exact historical development is uncertain, but the structure suggests a phono-semantic compound where the heart radical indicates an emotion.
The heart radical 忄 beside 長 (long) suggests a sadness that stretches on for a long time. Picture a heart weighed down by a long, lingering disappointment.
For チョウ, imagine a person named Chou who always looks sad and disappointed. Chou -> チョウ, and his long face shows the lingering sadness of 悵.
disappointed; upset; sad; sorrowful