1.The number four. (Poetic)
2.A set of four parts, things, or person; four things taken collectively; a group of four words, phrases, circumstances, facts, or the like. "Delivered him to four quaternions of soldiers." "Ye elements, the eldest birth Of Nature's womb, that in quaternion run." "The triads and quaternions with which he loaded his sentences."
3.A word of four syllables; a quadrisyllable.
4.(Math.) The quotient of two vectors, or of two directed right lines in space, considered as depending on four geometrical elements, and as expressible by an algebraic symbol of quadrinomial form. Note: The science or calculus of quaternions is a new mathematical method, in which the conception of a quaternion is unfolded and symbolically expressed, and is applied to various classes of algebraical, geometrical, and physical questions, so as to discover theorems, and to arrive at the solution of problems.
