这一概念深奥，在专业争论之外很少使用。

The notion is ___arcane and rarely used outside specialist debates.

这位教授精通一些只有少数人懂的秘传知识。

The professor mastered some ___arcane knowledge understood by only a few.

这些古老的符号对现代人来说非常晦涩难懂。

These ancient symbols seem ___arcane to modern people.