Source : Webster's Revised Unabridged Dictionary (1913)

Sesquiduplicate \Ses`qui*du"pli*cate\, a. [Sesqui- + duplicate.]
   Twice and a half as great (as another thing); having the
   ratio of two and a half to one.

   {Sesquiduplicate ratio} (Math.), the ratio of two and a half
      to one, or one in which the greater term contains the
      lesser twice and a half, as that of 50 to 20.