Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
invulnĕrābĭlis, e, adj., invulnerable: hostis, Sen. Ben. 5, 5, 1.
Transf.: cum animum virtus induravit, undique invulnerabilem praestat, Sen. Cons. ad Helv. 13, 2; id. Ep. 9, 2.