Sesquiduplicate

Ses`qui`du´pli`cate

a.

1.

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.

Webster's Revised Unabridged Dictionary, published 1913 by G. & C. Merriam Co.