缩

Left radical 纟 is the simplified silk/thread form of 糸. It marks 缩 as a thread-action: tightening, drawing in, contracting like a pulled drawstring. The silk radical groups 缩 with the textile family - 织 (weave), 纺 (spin), 绑 (tie), 紧 (tight) - all dealing with how threads pull and bind.

Right phonetic 宿 supplies the sound - sù shifted to suō via vowel rounding, a regular variation. Faint semantic flavour bleeds through: 宿 means 'pull in for the night, settle down', which matches the contracting/withdrawing sense of 缩. Same phonetic in 缩 alone, but 宿 itself appears widely in 宿舍 (dormitory), 住宿 (stay).