Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
Sergestus, i, m., a steersman among the followers of Æneas; acc. to Vergil, the ancestor of the Sergian family, Verg. A. 1, 510; 5, 121; 5, 184; 5, 221 et saep.