Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
† mĕgistānes, um, m., = μεγιστᾶνες the grandees of a kingdom, the magnates who were in the king’s suite, Sen. Ep. 21, 4; Tac. A. 15, 27; Suet. Calig. 5.