More can be written, but you might like to read 'Why do American high schools and universities use the nomenclature "freshman, sophomore, junior, senior" instead of, e.g., 1st-year, 2nd-year, etc.? How did that develop?' , by /u/sunagainstgold and /u/UrAccountabilibuddy (best in that order, because sunagainstgold covers earlier use and UrAccountabilibuddy covers later use).

This is not to discourage discussion. Further questions, data, and debate are welcome.