Thin

gầy

(having little body fat or flesh; slim; slender; lean; gaunt)

loãng

(of low viscosity or low specific gravity — see also watery, liquidy, diluted)

mảnh

(having little thickness or extent from one surface to its opposite)

mỏng

(having little thickness or extent from one surface to its opposite)

ốm

(having little body fat or flesh; slim; slender; lean; gaunt)