long feathers, scraggy
毿 centers on long, scraggly hair or feathers: something thin, wispy, and unkempt. The two given meanings are closely related, both describing a ragged, elongated texture.
毿 combines 毛 (hair/fur) with 參, which likely contributes the sound and may suggest a sense of mixing or irregularity, together giving the idea of long, scraggly hair or feathers.
The right side is 毛 (hair), and the left side 參 looks like a tangled, messy shape. Picture a bird with long, scraggly feathers that look like uncombed hair.
For サン, imagine the scraggly feathers of a bird basking in the sun: sun -> サン, and the sun highlights every long, messy strand.