'adelphoi' originates from Greek, specifically the word 'ἀδελφοί', where 'ἀδελφός' meant 'brother'.

'ἀδελφοί' was used in early Christian texts to denote a group of brothers or brethren, and it has been adopted into English theological discussions.

Initially, it meant 'brothers' in a familial sense, but over time it evolved to include a broader spiritual brotherhood.