index -- (a numerical scale used to compare variables with one another or with some reference number)
index, index number, indicant, indicator -- (a number or ratio (a value on a scale of measurement) derived from a series of observed facts; can reveal relative changes as a function of time)
exponent, power, index -- (a mathematical notation indicating the number of times a quantity is multiplied by itself)
index -- (an alphabetical listing of names and topics along with page numbers where they are discussed)