My final-year students are graduating today. They'll be graduands for the duration of the morning and afternoon, and by around 3.30pm they'll be graduates. I enjoy this use of Latin morphology: the -and ending comes from the Latin gerund and gerundives, which end in -andum or -andus/-anda/-andum respectively.
The gerund is a noun derived from a verb, so in English it would be something like Graduating is a reason to celebrate. The gerundive is an adjective, and it's translated as something like 'to be graduated' (or 'fit to be graduated' or 'ought to be graduated'). It's this gerundive sense that we use in English: they are the students who are (fit) to be graduated. (Notice that we're using an adjective to refer to a thing, as in 'the French'.)
It appears that we've knocked off the gender agreement ending (-us, -a, or -um) and this helps us out in English so that we don't have to worry about whether it's a male or female graduand. Incidentally, when we borrowed this word into English I'm pretty sure they'd have all been chaps so I don't think this was gender equality at work.
When the graduands morph into graduates, they also become alumni, another Latin word. It's plural, in that form, and pedants will have know that the singular is alumnus or alumna, depending on whether you're male or female. Again, this is a bit annoying for English speakers who don't really bother that much with gender other than pronouns, and even there we're not fully signed up to a gendered system (we make no distinction other than for singular humans that aren't me or you (he and she, in other words), and singular they is also available if we can't be bothered even with that).
Normal procedure when removing gender distinction is to go with the male for everyone: actors and actresses become actors, lady doctors become doctors, and so on. With alumni, we're taking to using the plural form for everyone. You're an alumni once you graduate. This ever so slightly grates on me but I am a good linguist and a descriptivist and do not go around correcting people. I don't know why we use the plural. We're familiar with this in words like cactus/cacti so we might have used alumnus as the singular; we just didn't. Perhaps it's because we use alumni in the plural way more often than the singular and, as it's not that common a word, that's the one that stuck.