Definition of: quaternion

(kwə·tûr′nē·ən) noun
1. A set, system, or file of four.
2. Math. a An operator or factor that changes one vector into another: so called because expressible as the sum of four quantities. b The form of the calculus of vectors based on and making use of the quaternion operator. [<LL quaternio, -onis <quattuor four]