mean proportional
/ˌmiːn prəˈpɔːʃ(ə)n(ə)l/ /ˌmiːn prəˈpɔːʃən(ə)l/Mathematics and Geometry
noun
A quantity related to two given quantities in such a way that dividing it by the smaller gives the same result as dividing the larger by it; the geometric mean of two quantities.
Origin
Late Middle English; earliest use found in Art Nombryng. Originally from mean + proportional; later reinterpreted as from mean + proportional.