Fluence

Part of speech: noun

Definitions

1. A measure of the total radiation or particles passing through a given area over a period of time ; an older term for a steady flowing or flux of something
2. The amount of energy or particles delivered across a surface during an exposure ; a dated word for the act or quality of flowing
3. The quantity of radiation that strikes each unit of an area during a set time ; an obsolete sense meaning a continuous stream or flux

Etymology: The word "fluence" in its physics sense, radiation passing through a given area, is a clipped form of "influence," which is a surprising fact about a word that now sounds like a separate creature altogether. "Influence" came into English from Old French and originally belonged to astrology: it named the supposed flowing of invisible force from the stars onto human affairs, and the Latin "influere" meant "to flow into." Over centuries the word lost that cosmic sense and drifted toward the general idea of power over others. The shorter form was taken up in the sense of a stream of something flowing through a space, which is how it came to describe the amount of radiation crossing a surface. The word was borrowed from French "fluence," which carries the same flowing idea, so the modern scientific use stays close to the word's original image of something streaming through.