According to my Longman Dictionary of Contemporary English, the word "Professor" is a countable noun. However, one of its examples reads:
professor a teacher in a college or university. In Britain, a professor is a high-ranking university teacher, especially one who is head of a department.
She was professor of linguistics at Cambridge University.
"She was professor ..." or "She was a professor ..."? Is this a difference between American and British usage?
Another Example from a website of Prof. Tony McEnery: Link
I am Distinguished Professor of English Language and Linguistics at Lancaster University.
Thank you in advance.