sesquiplicate

CIDE DICTIONARY

sesquiplicate, a. [Sesqui- + plicate.].

 Subduplicate of the triplicate; -- a term applied to ratios; thus, a and a′ are in the sesquiplicate ratio of b and b′, when a is to a′ as the square root of the cube of b is to the square root of the cube of b′, or a:a′::3:3.  [1913 Webster]
"The periodic times of the planets are in the sesquiplicate ratio of their mean distances."  [1913 Webster]