Abarim Publications' online Biblical Greek Dictionary
The noun αδελφος (adelphos) means brother (Matthew 1:2, Luke 3:1), or more generally, someone with whom one shares a common origin (Acts 3:22, Romans 9:3), or when used figuratively, a common perspective, objective or modus operandi (Matthew 12:50, Mark 10:29-30, Romans 8:29).
The feminine version of our word is αδελφη (adelphe). This word means sister with the same range of application as the masculine counterpart: from a female sibling (Luke 10:39) to a female fellow believer (Romans 16:1).
Our words are formed from the prefix α (a), in this case a collative denoting unity, and the noun δελφυς (delphus), meaning womb (this word is not used in the Bible), and yield the following derivations:
- The noun αδελφοτης (adelphotes), meaning brotherhood (1 Peter 2:17 and 5:9 only).
- Together with the adjective φιλος (philos), meaning beloved or friend: the adjective φιλαδελφος (philadelphos), meaning brother-loving (1 Peter 3:8 only). From this noun derives:
- The noun φιλαδελφια (philadelphia), meaning brotherly love (Romans 12:10, 1 Thessalonians 4:9, Hebrews 13:1, 1 Peter 1:22 and 2 Peter 1:7).
- Together with the adjective ψευδης (pseudes), meaning false or deceptive: the noun ψευδαδελφος (pseudadelphos), meaning false or pseudo brother (Galatians 2:4).