One of the directors of a company is being appointed as chairman. He shall remain so for his life term. Is there a particular term/word to describe a person holding a position or office for life?
There's actually nothing in the Constitution that explicitly promises federal judges "lifetime appointments."
In academia, this is called being tenured.
That term isn't normally used in business, but the meaning would be unambiguous if used of a company chairman.
Elsewhere, whole-life-term appointments can be shown by just prefixing "life", for example a "life peer" in the UK's House of Lords.
However, the most standard way of expressing this is a phrase, rather than a single word: lifetime appointment