1. a secondary or subordinate index, especially one that is part of a larger index system
Usage: technical; publishing
2. in mathematics, a subscript or lower index used to identify elements in a sequence or array
Usage: mathematics

Examples

• The book’s subindex organized topics by chapter and page number.
• Each subindex contained references to specific themes within the main text.
• The database uses a subindex to speed up searches on secondary criteria.
• In the equation, x₁ has a subindex of 1 to distinguish it from other variables.
• The array element a[i][j] uses j as a subindex for the second dimension.
• Publishers often create a subindex for proper names mentioned in the work.