
noun a person who pleads for a cause or propounds an idea
advocator; proponent; advocate.

noun someone who expounds and interprets or explains

noun a mathematical notation indicating the number of times a quantity is multiplied by itself
index; power.
WordNet
Ex*po"nent noun
Etymology
L.
exponens,
entis, p. pr. of
exponere to put out, set forth, expose. See
Expound.
Definitions
 (Alg.) A number, letter, or any quantity written on the right hand of and above another quantity, and denoting how many times the latter is repeated as a factor to produce the power indicated; thus a2 denotes the second power, and an the xth power, of a (2 and x being the exponents). A fractional exponent, or index, is used to denote the root of a quantity. Thus, a⅓ denotes the third or cube root of a.
 One who, or that which, stands as an index or representative; as, the leader of a party is the exponent of its principles.
Webster 1913
Sharpen your Skills with the Masters
"Rowling never met an adverb she didn't like."
Stephen King on J.K Rowling's excessive use of adverbs.
Fear not the Adverb Hell!