My nine year old daughter asked me this question this morning and I didn’t have a clue. I promised her I would find out. Does anybody know the answer to this one?
It’s from Greek and means wise (sophos) idiot (moros). The name denotes the idea that students at that age think thee know everything, but don’t have a clue.
“Sophomore” combines the Greek words for “wise” and “foolish.” One who is a “sophomore” is both wise and foolish.
Cecil covered the etymology:
Note that the Staff Report (by bibliophage) debunks the sophos moros connection, saying it is a false etymology which has influenced the modern/“American” spelling.
bibliophage is a real smart guy, and I hate to contradict him, but I have to disagree. The Real[sup]TM[/sup] origin does have to do with what college students were called, but in a different way than what the Staff Report says.
This word comes from the days when college students would have to take a train from the West to the East Coast to go to school. Because they were just poor students, they usually had to take the least desirable seats on the train. Because the heat from the sun made them uncomfortable, these seats were on the south side of the train which were on the right side going to college and the left side coming home. So their tickets were stamped SOPH for Starboard Out, Port Home and students were sometimes called “sophs”.
After a while, it was noted that second year students tended to be the poorest college students. So they had to travel SOPH MORE than the others. Thus they became known as sophomores.
Cite?
Where’s a whooshie when you need one?
Ha…you’ve got to kidding about sophmores thinking they’re smart yet they don’t know everything…I’m going to be one this/next school year. I think anyone can be a sophmore…it’s probably just something parents have come up with to deal with their 15 and 16 year olds.
See specious etymology of “posh” to get the joke.
I got the joke. “Cite?” was mine. Guess we had a double whoosh. 
The word “sophomore” was applied exclusively to college for at least a century or so before it got down to the “high school” level.
Oi folks - so IS there a real answer? Cos I have sometimes wondered about this.
In exchange for dispelling my ignorance, I’ll even explalin about “bejantines”. 
The real answer is the one found in the Staff Report. “Sophomore” is a corruption of “sophumer.” The modern spelling is probably influenced by the idea that the word comes from Greek moros (meaning “fool”). “Sophumer” was a a variant of “sophister” or “sophist,” meaning a thinker, a scholar, or a person skilled in making arguments.
I have to say I like dtilque’s answer better though. It’s much more entertaining.
Thanks **Bibliophage
It should be noted that Merriam-Webster still has the wise-foolish etymology on their on-line dictionary. Maybe someone should forward the staff report to them.