This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
懏 combines 忄 (heart/mind) with 雋, which likely contributes sound. The exact historical development is uncertain.
The heart radical 忄 beside 雋 suggests a mental quality, but without a clear meaning, picture a heart trying to understand a complex, bird-like shape.
For シュン, imagine a heart (忄) that beats soon (シュン) after seeing the intricate 雋 shape: soon -> シュン.