This is something I have wondered for some time now: the word Antisemitism. It means being antijewish. The only thing is, “Semite” doesn’t just mean Jewish. I have a dictionary in front of me now that says Semite refers to Hebrews, Arabs, Assyrians, Phoenicians, “etc.” So how did antisemite come to refer to just Jewish people?
Thank you in advance to all who reply 
It was coined to refer to Jews only.
As the previous poster said the term was a deliberate attempt by 19th century anti-jewish bigots to transform anti-jewish religious prejudice into “scientific” racial prejudice.
By the 19th Century open religious prejudice had become quite “un-PC” in most educated European circles, with its pre-enlightment dark ages connotations. Where racial prejudice on the other hand was quite alright, and in fact, considered quite “scientific”.
I would think, though, for those original German anti-semites, that they weren’t any more favorably impressed with Arabs and other middle-eastern Semitic ethnicities, but there weren’t many Arabs in their backyard at the time, while the Jew population in Germany was much higher. That would seem to be an important factor in the connotation that the word has today, especially how we’ve gotten to the point where Arabs can be accused of anti-semitism.
[sub](My $0.02 worth is all WAG)[/sub]
Just as a general rule, the technical meaning of the origin of a word seldom has anything to do with the meanings that the word has accrued over the years.
Although anti-semitism was coined, it’s little different in not being a literal translation of its root words than the vast majority of other words that you use every day.
I notice the people who can’t understand how antisemitism means jew hatred have no problem with the idea that awful and awesome have opposite meanings–today.
I think this must have been a factor.