Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
Vaccus, i, m.; Vitruvius Vaccus, a general of Fundi, taken captive by L. Papirius. The vacant site of his house at Rome was called Vacci prata, Liv. 8, 19 sq.; Cic. Dom. 38, 101.