This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
The exact historical development is uncertain. The modern form combines 函 and 頁, but the original semantic and phonetic roles are unclear.
The left side 函 suggests a box or container, and the right side 頁 relates to the head. Picture a box-like shape around the head, but the exact meaning is unclear.
For カン, imagine a can (カン) placed on the head, matching the 頁 (head) component.