The word kike () is an ethnic slur for a Jew.
Etymology
The earliest recorded use of the word dates to the 1880s.According to the Oxford English Dictionary, it may be an alteration of the endings –ki or –ky common in the personal names of Jews in eastern Europe who immigrated to the United States in the early 20th century. A variation or expansion of this theory published in Our Crowd, by Stephen Birmingham, postulates that the term "kike" was coined as a put-down by the assimilated U.S. Jews from Germany to identify eastern European and Russian Jews: "Because many Russian [Jewish] names ended in 'ki', they were called 'kikes'—a German Jewish contribution to the American vernacular. The name then proceeded to be co-opted by non-Jews as it gained prominence in its usage in society, and was later used as a general derogatory slur."
The Encyclopedia of Swearing suggests that Leo Rosten's suggestion is the most likely. He stated that:
The word kike was born on Ellis Island when there were Jewish...