noun the number four.
2. quaternion ·noun a word of four syllables; a quadrisyllable.
3. quaternion ·vt to divide into quaternions, files, or companies.
4. quaternion ·noun a set of four parts, things, or person; four things taken collectively; a group of four words, phrases, circumstances, facts, or the like.
5. quaternion ·noun 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.