poly·ad I. \ˈpälēˌad\noun (-s) Etymology:poly- + -ad 1.: a group consisting of several closely related parts or elements 2.: a polyad atom, radical, or element II. adjective 1.orpoly·ad·ic\| ̷ ̷ ̷ ̷|adik\: of, relating to, or constituting a polyad 2.[poly- + -ad]: polyvalent