tetrad

A group of four things.

Two pairs of sister chromatids (a dyad pair) aligned in a certain way and often on the equatorial plane during the meiosis process.

A group of four haploid and immature pollen grains in tetrahedral fashion produced by meiotic microsporogenesis.

A unit of land area of two by two (that is, four) square kilometres.

A tetravalent atom or radical.

A group of four basis vectors for a four-dimensional manifold in differential geometry.

A chord comprised of four notes; a tetrachord.