Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
† trĭērarchus, i, m., = τριήραρχος, the captain of a trireme, a trierarch, Cic. Verr. 2, 1, 20, § 52; Tac. H. 2, 16; Suet. Ner. 34; Inscr. Orell. 2652; 3595; 3603; 3615 sq.