LATIN DICTIONARYLexicon Latīnum
proper noun · masculinesecond declension

Postumius1

Postumius m sg (genitive Postumiī or Postumī)
Classical[pɔsˈtʊ.mi.ʊs]Ecclesiastical[posˈtuː.mi.us]

Meaning

  1. masculinesingulara Roman praenomen or nomen gentile, gens or "family name" famously held by
  2. masculinesingularAulus Postumius Tubertus, a Roman military leader

Declension

declension
formsingularplural
nominativePostumius—
genitivePostumiī
Postumī
—
dativePostumiō—
accusativePostumium—
ablativePostumiō—
vocativePostumī—

Postŭmĭus (erroneously writt. Post-hŭmĭus; v. postumus, under posterus, III. B.), i, m.; Postŭmia, ae, f.,
I. name of a Roman gens.
I. Postumius Tubertus, a Roman consul, Liv. 2, 16.—
II. Postumia, wife of Sulpicius, Cic. Fam. 4, 2, 1.—
III. A Vestal, Liv. 4, 44.—
IV. A woman addicted to tippling, Cat. 27, 3.—Hence,
A. Po-stŭmĭus, a, um, adj., Postumian: lex, Plin. 14, 12, 14, § 88: via, leading towards Genoa, Tac. H. 3, 21.—
B. Postŭmĭā-nus, a, um, adj., of or belonging to a Postumius, Postumian: imperia, i. e. of the dictator A. Postumius Tubertus, Gell. 1, 13, 7; Liv. 4, 29: caedes, i. e. of M. Postumius Regillensis, id. 4, 51.

Origins

From postumus. As a praenomen, it originally referred to children whose father died before they were born and were thus posthumous.

In the Academy Smith's classical dictionaries

adjectivefirst/second-declension adjective
Postumius2
Postumius (feminine Postumia, neuter Postumium)
Classical[pɔsˈtʊ.mi.ʊs]Ecclesiastical[posˈtuː.mi.us]

Meaning

  1. adjectiveof or pertaining to the gens Postumia.

Declension

singular
formmasculinefeminineneuter
nominativePostumiusPostumiaPostumium
genitivePostumiīPostumiaePostumiī
dativePostumiōPostumiaePostumiō
accusativePostumiumPostumiamPostumium
ablativePostumiōPostumiāPostumiō
vocativePostumiePostumiaPostumium
plural
formmasculinefeminineneuter
nominativePostumiīPostumiaePostumia
genitivePostumiōrumPostumiārumPostumiōrum
dativePostumiīsPostumiīsPostumiīs
accusativePostumiōsPostumiāsPostumia
ablativePostumiīsPostumiīsPostumiīs
vocativePostumiīPostumiaePostumia

Origins

From postumus. As a praenomen, it originally referred to children whose father died before they were born and were thus posthumous.

In the Academy Smith's classical dictionaries

Quick answers

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