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 a common perspective, objective or modus operandi (Matthew 12:50, Mark 10:29-30, Romans 8:29; see our article on the word υιος, huios, meaning son for a discussion of the use of this word for these more general relationships).
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), which in this case is a collative which denotes unity, and the noun δελφυς (delphus), meaning womb (this word is not used in the Bible).
Our noun(s) yield the following derivatives:
- 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).