sesquiplicate

a. [ Sesqui- + plicate. ] (Math.) 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′::√b3:√b′3. [ 1913 Webster ]

The periodic times of the planets are in the sesquiplicate ratio of their mean distances. Sir I. Newton. [ 1913 Webster ]