Main Entry: qua·ter·ni·on

Pronunciation: \kwə-ˈtər-nē-ən, kwä-\

Function: noun

Etymology: Middle English quaternyoun, from Late Latin quaternion-, quaternio, from Latin quaterni four each, from quater four times; akin to Latin quattuor four — more at four

Date: 14th century

1 : a set of four parts, things, or persons
2 : any of a set of numbers that comprise a four-dimensional vector space with a basis consisting of the real number 1 and three imaginary units i, j, k, that follow special rules of multiplication, and that are used especially in computer graphics, robotics, and animation to rotate objects in three dimensions