Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
lĭmĕnarcha, ae, m. [vox hybrida; limen, ἄρχω; cf. Germ. Markgraf; Engl. margrave], a commander on the frontier: limenarchae et stationarii fugitivos deprehensos recte in custodiam retinent, Dig. 11, 4, 4; Paul. Sent. 1, 6, 3 (acc. to others, a harbor-master, port-warden).