Synonyms for Index (same or very similar meaning)
WordNet sense 1 (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):
indicator, indicant, index number
WordNet sense 2 (a mathematical notation indicating the number of times a quantity is multiplied by itself):
exponent, power
WordNet sense 3 (the finger next to the thumb):
forefinger, index finger
From the ODE community, based on WordNet
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