Hands pointing to text in square after cubes

• Back-of-the-book readings
• Alphabetical listings
• Cookbooks have them
• Signs I’d since altered
• Catalogues
• Textbook adjuncts
• Market measurements
• The Dow and the Nikkei

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)]

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.