This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
賰 combines 貝 (shell/money) with 春 (spring), but the exact historical development and original meaning are uncertain.
With 貝 (money) and 春 (spring), imagine a springtime market where shells are used as currency, but the true meaning is unclear.
For シュン, picture a spring market where you soon spend your shells: soon -> シュン.