for·men·kreis \ˈfȯrmənˌkrīs\noun (pluralformenkrei·se \-īzə\ ; orformenkreis·es \-īsə̇z\) Etymology: German, literally, cycle of forms, from formen, plural of form (from Middle High German forme, from Latin forma) + kreis circle, cycle — more at form, artenkreis : a polytypic species (as of birds)