Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
Ventĭdĭānus, a, um, v. Ventidius.
Ventĭdĭus, i, m., the name of a Roman gens; so P. Ventidius Bassus, a partisan of Antony, Cic. Phil. 12, 9, 23; 13, 11, 26; 13, 21, 48; 14, 7, 21; Planc. ap. Cic. Fam. 10, 18, 3; Gell. 15, 4.
Hence, adj.: Ventĭdĭā-nus, a, um, Ventidian, of Ventidius: milites, Brut. ap. Cic. Fam. 11, 13, 3: rumores, Cic. Fragm. ap. Non. 92, 21.