mourning
絻 centers on mourning, specifically the ritual garments or cloth associated with funerals and remembrance of the dead.
絻 combines 糸 (thread, cloth) with 免, which likely contributes the sound and may relate to the idea of avoidance or removal, as in mourning rituals. The exact historical development is uncertain.
The left side 糸 is thread or cloth, and the right side 免 can suggest exemption or release. Picture mourning clothes made of coarse thread, worn when one is released from ordinary life to honor the dead.
For ブン, imagine a funeral bun (a small bread roll) left as an offering on the mourning cloth: bun -> ブン, tying the sound to the somber scene.