What do you normally call a teacher or professor who is very sever in punishing students in the class and tries to give the hardest exams to the students?
The adjectives that comes to mind are "strict", "stern" and "severe". In other hand Google Ngram shows that for the noun "teacher" , strict is the best choice and for the noun "professor" the adjective "stern" stands out.
It was what came to my nonnative mind, but what a native speaker would say in everyday English in what made me to ask this question. Now please let me know what are the most common combinations for the nouns "professor" and "teacher".