Brethren are fellow members of a religious or close community. Dear brethren, the brethren, our brethren.
It is the older plural of brother, kept for religious and fraternal use where brothers means family. Churches, monastic orders and organisations like the Plymouth Brethren use it. It is also used ironically for colleagues: our brethren in the press. Note that English keeps a few of these old -en plurals — children, oxen — and that brethren is the only one with a rival plural in daily use.
1nounbrethrenFellow members of a religious or close community.
“The old monk welcomed us and introduced us to his brethren.”
brethren is fellow members.
Brethren is the older plural of brother, formed with the -en ending that also gives children and oxen. Brothers replaced it for family, leaving brethren to the church.
Middle English
brethren
English, today
brethren
Built from
From Early Modern English brethren, plural of brother, from Middle English brethren, from Middle English brethere, brether + -en. Ultimately from Old English brōþor, brōþru (“brothers, brethren”), influenced by Old English brēþer, dative singular of brōþor (“brother”). Equivalent to brother + -en. Compare German Brüder (“brothers, brethren”). More at brother. The vowel change (from o to e) is called umlaut.
Etymology from Wiktionary, CC BY-SA