Tough

bền

(material science: undergoing plastic deformation before breaking)

dai

(difficult to chew)

du côn

(rowdy or rough)

dẻo

(material science: undergoing plastic deformation before breaking)

dẻo dai

(rugged or physically hardy)

khó

(difficult or demanding)

khó nhai

(difficult to chew)

khắc nghiệt

(harsh or severe)

mạnh mẽ

(rugged or physically hardy)

ngoan cố

(difficult or demanding)