exponent

Concise Oxford English Dictionary © 2008 Oxford University Press:
exponent /ɪkˈspəʊnənt, ɛk-/

▶noun

• 1 a promoter of an idea or theory.

• 2 a person who does a particular thing skilfully.

• 3 Mathematics the power to which a given number or expression is raised (e.g. 3 in 2³ = 2 × 2 × 2).

• 4 Linguistics a linguistic unit that realizes another, more abstract unit.

– origin C16 (as adj. in the sense ‘expounding’): from L. exponent-, exponere (see expound).