n. A set, group, or body of four: applied to persons or things.n. A word of four syllables; a quadrisyllable.n. A fourfold quantity capable of being expressed in the form xi + yj + zk + w, where x, y, z, w are scalars, or real numbers, while i, j, k are vectors, or quantities whose squares are negative scalars. The calculus of such quantities is termed quaternions.To divide into quaternions, files, or companies.n. In book-making, a set or ‘gathering’ of four sheets of paper or parchment folded in two.