Linguistic Question of the Week

Two definitions from the Merriam-Webster dictionary…

Main Entry: Sem·ite
Pronunciation: ’se-”mIt, esp British ’sE-”mIt
Function: noun
Etymology: French sémite, from Semitic Shem, from Late Latin, from Greek SEm, from Hebrew ShEm
Date: 1848
1 a : a member of any of a number of peoples of ancient southwestern Asia, including the Akkadians, Phoenicians, Hebrews, and Arabs
b : a descendant of these peoples

Main Entry: an·ti-Sem·i·tism
Pronunciation: “an-ti-’se-m&-”ti-z&m, “an-”tI-
Function: noun
Date: 1882
: hostility toward or discrimination against Jews as a religious, ethnic, or racial group

Question: If Semites include “Hebrews and Arabs,” why is anti-Semitism just “hostility toward or discrimination against Jews” instead of all Semites?