This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
浞 is a rare character combining 氵 (water) and 足 (foot/leg). The exact historical development is uncertain.
Water 氵 beside a foot 足 suggests stepping into water, but the actual meaning is unclear.
For サク, imagine stepping into a sack of water: sack -> サク, with your foot getting wet.