What is the meaning of the word "chair"?

Definitions:

a particular seat in an orchestra noun
- They are second chair violin.
a seat for one person, with a support for the back noun
- They put their coat over the back of the chair and sat down.
the officer who presides at the meetings of an organization noun
- address your remarks to the chairperson
the position of professor noun
- I was awarded an endowed chair in economics.
to act or preside as chair, as of an academic department in a university verb
- I chaired the department for many years.
to preside over verb
- I volunteered to chair the committee.