What does Posīdōn mean in Latin?

Posīdōn, a proper noun, means “Poseidon”.

What is the genitive of Posīdōn?

The genitive singular is Posīdōnis. Posīdōn is masculine, third declension.

In classical Latin, [pɔˈsiː.doːn]; in ecclesiastical (church) Latin, [poˈs̬iː.don].

proper noun · masculinethird declension

Posīdōn m sg (genitive Posīdōnis)

Classical[pɔˈsiː.doːn]Ecclesiastical[poˈs̬iː.don]

GreekNew LatinPoseidon
Atque ex descriptione Prokeschii templum Posidonis Theraei in promontorio supparem situm habuit in speluncâ; cuius in petrae fragminibus nomina insculpta sunt innumerabilia.1840, Johannes Franz, Elementa epigraphices Graecae, →OCLC, page 54:
[…]injuria autem Droysenius verba γαιήοχε κυανοχαῖτα, quae omnino non significant premit, cum ne tunc quidem condicio rerum talis fuerit, ut Aegyptii ipsi Antigonum Posidonem appellaverint.1890, Johannes Teufer, De Homero in apophthegmatis usurpato, →OCLC, page 11:

Borrowed from Ancient Greek Ποσειδῶν (Poseidôn).