Four.

A surname.

plural of Quadri

(rare) A grouping of four things. / (US) A government committee of four economic experts.

(mathematics) The lines of a 3-dimensional projective space, S, can be viewed as points of a 5-dimensional projective space, T. In that 5-space, the points that represent each line in S lie on a hyperbolic quadric, Q, known as the Klein quadric.

(physics) Synonym of four-acceleration

Supporting four frequency bands

(chemistry) tetrabasic

Alternative form of quadrable

plural of quadriad