Postumus is a Latin praenomen, or personal name, which was most common during the early centuries of the Roman Republic.
It gave rise to the patronymic gens Postumia, and later became a common cognomen, or surname.
[1][2][3] Postumus was used by both patrician and plebeian gentes, including the Aebutii, Antistii, Cominii, Livii, Mimesii, Plautii, Sempronii, Sulpicii, and Veturii; and naturally it must once have been used by the ancestors of gens Postumia.
Because it was not a common name, there are few examples of the feminine form, but Marcus Terentius Varro listed it together with other archaic praenomina that were no longer in general use by the 1st century BC, and Plutarchus mentions that it was given to the youngest daughter of the dictator Lucius Cornelius Sulla, who lived during Varro's time.
Naturally, this also applied to children born after the death of their father, and this coincidence is no doubt responsible for much of the confusion about the meaning of the praenomen.