What is pl. of Brother. Note: This form of the plural is used, for the most part, in solemn address, and in speaking of religious sects or fraternities, or their members called?

brethren — pl. of Brother. Note: This form of the plural is used, for the most part, in solemn address, and in speaking of religious sects or fraternities, or their members. (Webster's 1913.)

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