The Latin word meant a nursling or foster child, not a graduate.
The word alumni is the plural of the Latin alumnus, derived from the verb alere, meaning "to nourish" or "to feed."1 An alumnus was originally a nursling, a foster child, or a pupil who had been raised and nourished by another. The feminine form is alumna, with the plural alumnae. The word entered English in the seventeenth century in the educational sense.
In Roman usage, the word carried a personal dependency. An alumnus owed a debt to the household or patron who had nourished them. When English-speaking universities adopted the term, they preserved this transactional undertone. The expectation that graduates would give back to their institutions, through donations, mentorship, or reputation, echoes the original Latin relationship between nourisher and nourished.2
The modern alumni network emerged as universities expanded in the nineteenth century. Yale established one of the earliest formal alumni associations in the United States in 1821.3 Harvard and other institutions followed. These organizations formalized what the Latin word had already implied: the relationship between a campus and its former students does not end at graduation.
The gender-neutral singular "alum" and plural "alums" have gained currency in contemporary usage, replacing the gendered Latin forms. The original Latin verb, alere, meant to feed.