Left silk radical, the simplified 3-stroke form of 糸. Indexes 缚 in the threads-and-cords family (绳 rope, 线 thread, 织 weave) and supplies the meaning: binding someone with cord or ribbon, hence the extended sense of fettering or restraining.
Right 尃 — a hand 寸 spreading something out — supplies the sound fū → fù. The same phonetic frame sits inside 博 broad, 傅 tutor, 搏 to grapple, 缚 here. Knowing 尃 unlocks the whole bó/fù family of readings.
