Here's why:
* It ends in "-eur", which is a common masculine ending in French. Other examples include "acteur" (actor), "chanteur" (singer), and "vendeur" (seller).
* The feminine form is "professeure". It's important to use the correct gender agreement in French, especially with titles and professions.
So, you would say:
* "Le professeur" (the male professor)
* "La professeure" (the female professor)