The quality or state of being an exponent; the property of serving as an indicator or representative.
From exponent (something that expounds or represents) + -cy suffix. Rare formation creating an abstract noun for the function or quality of representing or indicating.
This word is so rare it barely exists in modern English, but it captures something useful: the 'exponency' of a symbol is its power to represent or stand for something else. All language rests on this principle.
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