Alumni is a plural noun referring either to a group male graduates or to a group of both male and female graduates. The singular alumnus refers to one male graduate, alumna refers to one female graduate, and the plural alumnae refers to a group of female graduates. These Latin loanwords preserve their original plural forms, and incorrect use of the words abounds because many speakers of English are understandably unfamiliar with the genders and plurals of Latin nouns.
If you have trouble keeping track of them all, one alternative is to use alum and alums. These increasingly appear as replacements for the traditional words—though they may be considered out of place in formal contexts—and they have the extra virtue of being ungendered and hence unconfusing.
These writers use the Latin forms correctly:
Durkee is one of 31 gay and lesbian Westmont alumni who earlier this month roiled the Christian college in Montecito with an open letter in the college newspaper. [Los Angeles Times]
ast month the Sonoma Valley High School girls’ basketball and volleyball programs held their second annual, and enjoyable, alumnae doubleheader in Pfeiffer Gym. [Sonoma News]
Rundle College alumnus Aaron Goodarzi can’t say enough about the advantages of independent schooling. [Calgary Herald]
Berklee alumna and faculty member Daniela Schächter will also give a guest performance. [Boston Globe]
And these writers opt to use the modern shortened forms:
The designer of the new Cowboys Stadium is an alum of Skyline’s architecture program. [Dallas Morning News]
He’s talented, but if he’s to add his name to an illustrious list of Hopeful alums who have gone on to classic success, he’ll have to buck some more recent history. [The Saratogian]