Merriam-Webster Collegiate Dictionary - exponent

 noun  Etymology: Latin ~-, exponens, present participle of exponere — more at expose  Date: 1706  1. a symbol written above and to the right of a mathematical expression to indicate the operation of raising to a power  2.  a. one that expounds or interprets  b. one that champions, practices, or exemplifies EXPONENTIAL FUNCTION  noun  Date: 1879 a mathematical function in which an independent variable appears in one of the exponents — called also exponential