Alumnus, alumni, etc.

Mary Vanderpool asked if the plural of the noun "alumnus" can be "alumnuses."

Thanks for the question about these difficult words!

Alumnus is defined in Merriam-Webster's Learner's Dictionary as, "someone who was a student at a particular school, college, or university." The plural of alumnus is alumni. Alumni used to be used for men only, but this is no longer true.

Alumna is defined as a "woman who was a student at a particular school, college, or university." The plural of alumna is alumnae, and it is still used for women, only. 

The form you asked about, alumnuses, is considered incorrect by most people.

I hope this helps.