不易 | bù yì | not easy to do sth / difficult / unchanging | |
不渝 | bù yú | constant / unchanging / abiding / faithful | |
坚贞不屈 | jiān zhēn bù qū | faithful and unchanging (idiom) / steadfast | |
亘古不变 | gèn gǔ bù biàn | unchanging since times immemorial (idiom) / unalterable / unvarying / monotonous |