Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
† mĕtŏpa, ae, f., = μετόπη, the space between two hollows; in architecture, the space between two dentils or two triglyphs, a metope (only in Vitr.): inter denticulos et inter triglyphos quae sunt intervalla, metopae nominantur, etc., Vitr. 4, 2, 4.