Green’s Dictionary of Slang

a professor, i.e. male teacher.

1908		DN III 310: Fesser. . . Professor. . . Every man that teaches is called a professor.
1930		‘Handed-down Campus Expressions’ AS VI:2 129: ‘Fessor’ is in common use, even by the townsfolk. ‘’Fess’ is less commonly, yet frequently heard.
1965–70		in DARE.
1976		A. Garber Mountain-ese 29: The fessor called Johnny inter his office fer throwin’ spitballs [HDAS].
2003		at www.unt.edu 🌐 Thomas P. Sovik, associate professor of music, won the 2002 ’Fessor Graham Award, the highest honor bestowed by the student body at UNT. [...] It is named for the late Professor Floyd Graham.