hard-and-fast 不容变更的;严格的hard-and-fast
Adjective (来源：2HZZ常识网 http://www.
2hzz.
com) strictly enforced (as of rules)
to stick to hard-and-fast rules 不容变更的;严格的
His parents have no hard-and-fast rules about how late he can stay out.

他的父母对他在外可以逗留多晚并没有严格的规定。
He stuck hard and fast to his principles.

他严守自己的信条。