The English word “Jew” is derived from Hebrew yĕhûdî (fem. yĕhûdît, “Judith”; see Gen. 26.34; also the book of Judith), meaning “Judean,” by way of Greek ioudaios and Latin judaeus. The term is first used of citizens of the southern kingdom of Judah in 2 Kings 16.6; previously, male inhabitants of the kingdom, or of the tribe of Judah from which the kingdom took its name, were referred to as ʾîš yĕhûdâ, literally “man [men] of Judah” (e.g., 1 Sam. 11.8). As a consequence of the exile of many members of the upper classes of Judah by the Babylonians in 597 and 587/586 BCE, many Jews were forcibly settled in Mesopotamia (2 Kings 24–25; Jer. 52). Others, including the prophet Jeremiah, fled to Egypt (Jer. 43). This was the beginning of the Jewish dispersion, or Diaspora, across the globe, which continues to this day. After the exile the term Jew came to be used for all descended from or identified with this ethnic or religious group, whatever their race or nationality. Thus, in Esther 2.5, Mordecai is identified both as a Jew and as a member of the tribe of Benjamin. The term “Jew” thus began to parallel the much more ancient designation “Israelite.”

The Jews who returned from exile after 538 BCE (Ezra 2; Neh. 7.6–73) settled in the Persian province of Yehud, which eventually became the Roman province of Judea and preserved its name until it was suppressed by the Romans in reaction to Jewish revolts of 66–73 and 132–135 CE.

In the New Testament “Jew” can designate both Jesus (Mark 15.2) and many of his followers (Acts 21.39), as well as some of his adversaries (1 Thess. 2.14–16). However, the rivalry between Christianity and Judaism, coupled with the often uncomplimentary portrait of Jews in the New Testament and the similarity in sound to the name of Judas, often made the word Jew pejorative in the Christian world (see Anti‐Semitism).

The question of how to define a Jew, put more simply as “who is a Jew,” has engendered much discussion through the ages. Are the Jews to be understood as a social, religious, national, or ethnic community? Basically, the answer of the Jewish tradition, the halakhah, has been that one born of a Jewish mother or one converted to Judaism is a Jew. But this definition has been challenged in recent years. The murder of many of Jewish descent who, however, were not halakically Jewish during the Holocaust has raised questions regarding inclusion and exclusion in the Jewish community. The high court of Israel, in the Brother Daniel Rufeisen case, has ruled that an apostate from Judaism cannot apply for automatic citizenship as a Jew under the Law of Return. And in recent years the American Jewish Reform movement has attempted to redefine the term Jew to include, in addition to converts, anyone of Jewish descent, whether that descent be matrilineal (the halakhic position) or patrilineal (excluded by halakhah), who practices Judaism and identifies himself or herself as a Jew. A strict definition is therefore impossible to reach.

Carl S. Ehrlich