Hands pointing to text in square after cubes

• Scales of charges Spain introduced for third of Catalans
• Textbook adjuncts
• Mathematical exponents
• Back-of-the-book conveniences
• Book lists

Douglas Harper's Etymology Dictionary Word definitions in Douglas Harper's Etymology Dictionary
according to OED, the plural form of index preferable in scientific and mathematical senses of that word.

WordNet Word definitions in WordNet
v. list in an index provide with an index; "index the book" adjust through indexation; "The government indexes wages and prices" [also: indices (pl)]

The Collaborative International Dictionary Word definitions in The Collaborative International Dictionary
Index \In"dex\, n.; pl. E. Indexes , L. Indices (?). [L.: cf. F. index. See Indicate , Diction .] That which points out; that which shows, indicates, manifests, or discloses; as, the increasing unemployment rate is an index of how much the economy has slowed. ...