In Latin, the plural form of the word is indices. In English, the plural "indices" is commonly used in mathematical and computing contexts, and sometimes in bibliographical contexts – for example, in the 17-volume Women in World History: A Biographical Encyclopedia (1999–2002). However, this form is now seen as an archaism by many writers and commentators, who prefer the anglicised plural "indexes". "Indexes" is widely used in the publishing industry; in the International Standard ISO 999, Information and documentation – Guidelines for the content, organization and presentation of indexes; and is preferred by the Oxford Style Manual. The Chicago Manual of Style allows both forms.
