Kike is a derogatory slur used to refer to a Jew

Jews

The Jews , also known as the Jewish people, are a nation and ethnoreligious group originating in the Israelites or Hebrews of the Ancient Near East. The Jewish ethnicity, nationality, and religion are strongly interrelated, as Judaism is the traditional faith of the Jewish nation...

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The source of the term is uncertain. According to the Oxford English Dictionary

Oxford English Dictionary

The Oxford English Dictionary , published by the Oxford University Press, is the self-styled premier dictionary of the English language. Two fully bound print editions of the OED have been published under its current name, in 1928 and 1989. The first edition was published in twelve volumes , and...

, 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

United States

The United States of America is a federal constitutional republic comprising fifty states and a federal district...

 in the early 20th century. The first recorded use of the term is in 1904.

According to Our Crowd

Our Crowd

Our Crowd is a book by Stephen Birmingham that documents the lives of prominent New York Jewish families of the 19th Century. Historian Louis Auchincloss called it "A fascinating and absorbing chapter of New York social and financial history..." There have been 14 editions of the book as of...

, by Stephen Birmingham

Stephen Birmingham

Stephen Birmingham, born May 28, 1932 in Hartford, Connecticut, is an author.Born to Thomas Birmingham and Editha Gardner Birmingham, he received a BA from Williams College in 1953. He is a former teacher of writing at the University of Cincinnati. He has written over thirty books and is now retired...

, the term "kike" was coined as a put-down by the assimilated U.S.