LATIN DICTIONARYLexicon Latīnum
proper noun · masculinesecond declension

Vespasius

Vespasius m sg (genitive Vespasiī or Vespasī)
Classical[wɛsˈpa.si.ʊs]Ecclesiastical[vesˈpaː.s̬i.us]

Meaning

  1. masculinesingulara Roman nomen gentile, gens or "family name" famously held by
  2. masculinesingularVespasius Pollio, the grandfather of Vespasianus

Declension

declension
formsingularplural
nominativeVespasius—
genitiveVespasiī
Vespasī		—
dativeVespasiō—
accusativeVespasium—
ablativeVespasiō—
vocativeVespasī—

Vespasĭus, i, m.; Vespasĭa, ae, f.,
I. the name of a Roman gens; e. g. Vespasia Polla, the mother of Vespasian, Suet. Vesp. 1: Vespasius Pollio, the father of Vespasia Polla, id. ib. 1.

Quick answers

What does Vespasius mean in Latin?
Vespasius, a proper noun, means “a Roman nomen gentile, gens or "family name" famously held by”.
What is the genitive of Vespasius?
The genitive singular is Vespasiī. Vespasius is masculine, second declension.
How do you pronounce Vespasius?
In classical Latin, [wɛsˈpa.si.ʊs]; in ecclesiastical (church) Latin, [vesˈpaː.s̬i.us].