The Chinese word for soap is
肥皂

féi zào

Chinese Definition

soap
1. 名词. 肥皂。
Components
肥
1. fat; plump; obese (adjective)
農場裡的小豬長zhǎng 得de 肥-肥的，好可愛。 - The pigs in the farm are quite plump, very cute.
一時嫌人肥，一時嫌人瘦，都唔知點好。 - Sometimes, I'm criticized for being fat, while other times, I'm criticized for being skinny. I don't know what to do.
2. fat; fatness (noun)
減肥 - to lose weight -
3. fertile
4. fertiliser
化肥 - chemical fertilizer -
氮肥 - nitrogenous fertilizer -
施肥 - to apply fertilizer -
5. (usually derogatory) benefit; advantage; gain
6. =====Usage notes=====
7. (Hong Kong Cantonese) to fail (a test)
8. (Hong Kong Cantonese) to fail (someone) in a test
皂
1. black
不分青紅皂白 - (literally) to not distinguish between blue-green, red, black and white.
2. Short for 皂斗, acorn
3. Short for 皂莢, (vern, Chinese honey locust)
4. soap
Synonyms: 肥皂
香皂 - scented soap
Synonyms: 差役

肥皂
1. n. soap
2. n. (obsolete) (vern, Chinese honey locust) (, or other similar plants, pounded into pieces)
Synonyms: 皂莢, 皂角
3. n. (slang) genocide victim