It used to be that you had to call the freshmen first-years. Now, there is a backlash against this terminology. The school still officially uses "first-year", but The Knox Student recently reverted back to the term freshman. I wish they hadn't.
First-year is considered more gender-neutral because it does not have the word "man" in it. First-year is also more literal than "freshman", as to prevent pretentious first-years with college credit from calling themselves sophomores.
There is no other term to describe this idea so that it is easily understood by everyone. If you say first-year, then I might rightly assume you are also talking about transfers or students who entered Knox with piles of AP credits that give them sophomore standing. This is, after all, their first year at the college. I would, however, be wrong. They are considered whatever their standing says they are. Therefore, freshman should be used to describe freshmen.