Polygonaceae po·ly·go·naceae uncommon noun 1. a family of plants of order Polygonales chiefly of the north temperate zone; includes the buckwheats Synonymsfamily Polygonaceaebuckwheat family Related words Broader terms dicot family Parts Polygonales Part of PolygonumFagopyrumgenus EriogonumRheumRumex WordNet 2.1 (Princeton University). WordNet 2.1 Copyright Princeton University. All rights reserved.