SESQUI-Alterate, in Geometry and Arithmetic, is a ratio between two lines, two numbers, or the like, where one of them contains the other once, with the addition of a half.
Thus 6 and 9 are in a sesqui-alterate ratio; since 9 contains 6 once, and 3, which is half of 6, over; and 20 and 30 are in the same; as 30 contains 20, and half 20 or 10.