quaternion

noun3

1. •
   A group or set of four people or things.
2. •
   A type of four-dimensional hypercomplex number consisting of a real part and three imaginary parts (real multiples of distinct, independent square roots of −1 denoted by i, j and k); commonly used in vector mathematics and as an alternative to matrix algebra in calculating the rotation of three-dimensional objects.

   • The right-hand side of the quaternion equation requires scalar multiplication and quaternion addition. — 2004
3. •
   A word of four syllables.