This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
The exact historical development is uncertain. The modern form visually combines 束 and 欠, but the original semantic and phonetic roles of these components are unclear.
The left side 束 suggests a bundle, and the right side 欠 suggests a person with mouth open. Picture a bundle being offered to a person, but the exact meaning is uncertain.
For サク, imagine a sack (サク) being tied around the bundle on the left, while the person on the right opens their mouth to receive it.