Two readings: cháng (literary, 'lower garment') as in 衣裳 in classical poetry, and shang (neutral tone) in the modern colloquial 衣裳 ('clothes'). In Old Chinese 衣 was the upper garment and 裳 the lower, the pair survives as the modern compound.
history
Appears in Li Bai's 《梦游天姥吟留别》 (霓为衣兮风为裳, 'rainbow as my robe, wind as my skirt') and in the imperial garment names 衮服霞裳.
Bottom 衣, pictograph of a garment with collar, sleeves, and hanging skirt panels. As the indexing radical it carries the meaning: 裳 is the lower garment, the long skirt worn from the waist down in classical dress. Same radical drives 袍 robe, 袖 sleeve, 裙 skirt.
Top 尚 supplies the sound, shàng drifting to cháng through a regular sh/ch shift visible in the same phonetic family: 常 constant, 偿 repay, 裳 garment, all share the same top. Adds no semantic content here, borrowed purely for pronunciation.
