The Chinese word for thin is
薄

báo

Chinese Definition

thin
1. 形容词. 瘦

薄
1. thin (not thick); flimsy
薄báo 布 - flimsy cloth
如履薄冰 - to be very careful, lit=like treading on thin ice
呢件衫好薄。 - This shirt is very light.
2. slight; meagre; small
薄酬 - small reward
3. poor; infertile
4. cold in manner; indifferent
5. ungenerous; unkind; mean
刻薄 - mean; unkind
6. (of taste) weak; light; not strong
酒味很薄báo。 - The wine is very weak.
7. to belittle; to despise
厚此薄彼 - to favour one and slight the other
8. Alternative form of 亳 (capital of Yin)
9. to reduce
10. (literary) to approach
日薄西山 - to approach death
^薄 ^一-波 - Bo Yibo
11. Only used in 薄荷 (mint)
12. Only used in 蓾薄

瘦
1. (of a person or animal) thin; slender; skinny
Antonyms: 胖, 肥
2. (of meat) lean
3. to lose weight; to become thin
Antonyms: 胖
他瘦了五公斤。 - He lost five kilograms.
4. (Min Nan) Alternative form of 㾪 (-)

細
1. (literary or Cantonese, Hakka, Min) small; tiny; little
Antonyms: 大
點解會咁細嘅ge2？ - Why is it so small?
2. thin; slender
Antonyms: 粗
細線 - thin string
3. fine; delicate; exquisite
Antonyms: 粗
細沙 - fine sand
4. careful; detailed; meticulous
5. slowly; carefully; thoroughly; detailedly
細看 - to carefully examine
6. trifling; trivial; unimportant
7. (of one's voice) soft
8. frugal; sparing
9. (literary or Cantonese, Hakka, Min) young; little
Antonyms: 大
你仲細咩！ - Do you think that you're still a child?
10. (Cantonese) to be younger than
Antonyms: 大
細佢幾十年 - younger than them by a couple decades
11. (Hokkien) concubine