noun
normal course; proper course; regular way
A formal noun for the normal, proper, or expected course of action or conduct. In modern usage it is especially common in negative or deviation expressions such as 常軌を逸する.
彼の発言は常軌を逸している。
His remarks are beyond the bounds of normal behavior.
混乱のあと、業務はようやく常軌に復した。
After the confusion, operations finally returned to their normal course.
常道 means the usual or proper method, especially in strategy or procedure; 常軌 is more about the bounds of normal conduct or course.
A Sino-Japanese compound: 常 means usual or constant, and 軌 means track, rule, or course. The spelling transparently matches the sense of a usual or proper course.