plural of tetrad

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

Of or relating to a tetrad. / (of a shape) Having four-fold symmetry; used especially of the digits 0, 1 and 8.

(rare, medicine) The tetralogy of Fallot.