Quick answer
Nereus is a boy name meaning "water, fresh".
Pronunciation: Classical Greek /nɛː.reú̯s/; English /ˈnɪɹ.i.əs/.
Meaning and history
This name is derived from Greek νηρός (neros) meaning "water, fresh". In Greek mythology he was a god of the sea, the father of the Nereids. The name is mentioned briefly in the New Testament, belonging to a Christian in Rome. This was also the name of a Roman saint of the 1st century, a member of the army, who was martyred with his companion Achilleus because they refused to execute Christians.
Notes and context
Usage: greek mythology, ancient greek, biblical, biblical latin, biblical greek | Ancient Greek: Νηρεύς