1 a set of four.
2 Math. a complex number of the form w + xi + yj + zk, where w, x, y, z are real numbers and i, j, k are imaginary units that satisfy certain conditions.
ME f. LL quaternio -onis (as QUATERNARY)
quaternity, four, tetrad, quartet, quaternion
, square, quarter, tetract, tetragon, quadrangle, rectangle, tetrahedron, quadrature, quadrifoil, quadriform, quadruplet, quatrefoil, tetrapod, quadrangle, quad, quadrupole, quadrivium, four, quaternary, quaternal, quadratic, quartile, tetract, tetractic, tetractinal, tetrad, tetragonal, square, quadrate.