Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
prŏ-nĕpos (scanned prōnĕpos, Sid. Carm. 11 fin.), ōtis, m., a great-grandson, Dig. 38, 10, 1; 38, 10, 14; Cic. Tusc. 3, 12, 26; id. Phil. 13, 7, 15; id. Att. 16, 14, 4; Ov. M. 10, 606.