sub·in·dex 
(sŭb-ĭndĕks)
(sŭb-ĭndĕks)n. pl. sub·in·di·ces (-dĭ-sēz′)
1. Mathematics A subscript.
2. pl. sub·in·dic·es or sub·in·dex·es An index of measurement based on relatively few variables, especially a trade index based on the performance of a particular group or type of stocks.