immutable       
adjective  formal uk/ɪˈmjuː.tə.bəl/ us/ɪˈmjuː.t̬ə.bəl/
 永恒的;不可改变的
not changing, or unable to be changed
  an immutable law 永恒的法则 
 Some people regard grammar as an immutable set of rules. 有些人认为语法是一套不可更改的规则。 
 Synonym: changeless 
Opposites: changeablemutable