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.

Source: Webster's Revised Unabridged Dictionary (1913)