The
衣 'clothing' radical wraps the outside of
衰 — top strokes form the collar, bottom strokes form the hem and dangling sleeves of a garment. It is the indexing radical and gives
衰 its concrete origin: a mourning robe of coarse fibre, woven from straw, with frayed strands inside. Same garment-wrap appears in
表 outer,
衷 inner,
哀 grief.