It’s graduation time and Sophie and I got curious about these words. For your etymological pleasure:
Freshman — “fresh” + “man”; Sense of “student in first year” attested from 1590s
Sophomore — from Greek sophumer, “arguer”; Sense of “student in second year,” attested from 1680s (“sopho” (wise) + “moro” (foolish), which I learned from my orthodontist years ago, is incorrect folk etymology and probably influenced the spelling)
Junior — from Latin for “younger”; Sense of “student in the third year” attested from 1862
Senior — from Latin for “older”; Sense of “student in fourth year” attested from 1741, from earlier general sense of “advanced student” attested from 1610s