Full Definition of EXPONENT. 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. See exponent defined for English-language learners.ull Definition of EXPONENT. 1. : a symbol written above and to the right of a mathematical expression to indicate the operation of raising to a power. 2.