A few words on the
origins of the term:
Remember Noah? He had three sons: Shem, Ham and Japheth. Since all the rest of humanity was destroyed in the Flood, it follows that all of present day mankind is descendent from one of the three of them. Naturally this geneaology doesn't take into account any nationalities which were not familiar to the writers of the ancient myth. In any case it is not a viable way of dividing people into groups, just a hangup from Biblical definitions. However, the "semitic" group remains, and modern day Jews and Arabs belong to it.
Anthropologically and archaeologically speaking, there were marked similarities in the cultures and languages of Semitic peoples of the ancient Near East. There were two groups of people called semitic - Eastern Semitic and Western Semitic. Aramaic and Accadian (the language of Assyria and Babylon) are Eastern Semitic languages, while Hebrew, Phoenician and Arabic are Western Semitic languages. Only the western branch of both semitic languages and cultures survives today.
Today, antisemitism has the dubious distinction of being a specialised term for Jew-hating.