Explanation:

The best choice that represents "one who holds a post without any salary" is "honorary."

- Highbrow: Refers to someone who is intellect-oriented or interested in high culture. It doesn't relate to holding an unpaid position.

- Volunteer: A person who offers to take part in an enterprise or undertake a task willingly. While volunteering is often unpaid, it's more about choice than holding a formal post.

- Samaritan: This refers to someone who is helpful or compassionate, especially to a stranger. It does not imply holding a specific post.

- Honorary: ?? Often used to describe a position that is held without monetary compensation, purely out of respect or recognition.