This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
懭 combines 忄 (heart) with 廣, which likely contributes the sound. The exact historical development is uncertain.
The heart radical 忄 beside 廣 suggests a feeling of vastness or emptiness, but the exact meaning is unclear.
For コウ, imagine a vast, empty heart (忄) echoing with a hollow sound: kou -> コウ.