When you have a Nobel Prize in Economics or a endowed professorship at the Univ.
From the economist.com
The funds will be used to create a distinguished professorship in epidemiology.
From the post-gazette.com
How do you get a professorship when your brain is so confused and inconsistent?
From the scienceblogs.com
He has held the Felix Frankfurter professorship at Harvard Law School since 1993.
From the economist.com
The university is moving ahead and interviewing candidates for the professorship.
From the economist.com
He also held a Fulbright professorship in Innsbruck in Austria from 1958 to 1959.
From the en.wikipedia.org
In December 1834, owing to continued opposition, he resigned his professorship.
From the en.wikipedia.org
I have added the distinguished professorship, which had been missing on the page.
From the en.wikipedia.org
The next year, the University of Turin also granted him his full professorship.
From the en.wikipedia.org
More examples
The position of professor; "he was awarded an endowed chair in economics"
A professor is a type of senior teacher; the precise meaning of the word varies by country. Literally, professor is Latin for a "person who professes to be an expert in some art or science, teacher of high rank" . ...
The office of a professor
Regular, salaried, benefit-eligible faculty identified annually by the appropriate administrator; the professorship may be renewable or non-renewable.