Opiter (/ˈoʊpɪtər/ or /ˈɒpɪtər/) is a Latin praenomen, or personal name, which was used primarily during the early centuries of the Roman Republic. It is not usually abbreviated, but is sometimes found with the abbreviation Opet., apparently based on an archaic spelling of the name. No examples of a feminine form used as a praenomen are known, but from a cognomen it appears to be Opita. The name gave rise to the patronymic gens Opiternia, and perhaps also gens Opetreia.
The praenomen Opiter was used by the patrician gentes Verginia and Lucretia, and several prominent members of these gentes with this name held important magistracies during the first two centuries of the Republic. The name must also have been used at one time by the ancestors of gens Opiternia. As with other rare praenomina, Opiter may have been more frequently used in the countryside. However, writing in the first century BC, Marcus Terentius Varro described it as obsolete.
The gens Opiternia may have been Faliscan, as a Faliscan named Lucius Opiternius is mentioned by the historian Livy. The Faliscan language was closely related to early Latin. A Latin inscription reading "OPI. SAUFIO L. L." may be interpreted as "Opiter Saufeius, freedman of Lucius," although Chase felt that the praenomen was probably Oppius. Despite the fact that both the Verginii and the Lucretii were of Etruscan origin, the praenomen Opiter does not appear to have been used by the Etruscans.