一成不变 yīchéngbùbiàn HSK7 set in stone Origin Definitions Defs Strokes Stroke Words Sentences Sents 一成 yīchéng once formed (bound form) once established or formed, used as in the phrase 一成不变 yīchéngbùbiàn不变 不變 bùbiàn adjectiveverb unchanging constant; unvarying; fixed; in mathematics, this refers to an invariant