Also see definition of "Brotherhood" in Word Study
Study Dictionary
Brotherhood
BROTHERHOOD [ISBE]
BROTHERHOOD - bruth'-er-hood: The rare occurrence of the term (only Zec 11:14 and 1 Pet 2:17) in contrast with the abundant use of "brother," "brethren," seems to indicate that the sense of the vital relation naturally called for the most concrete expression: "the brethren." But in 1 Pet 2:17 the abstract is used for the concrete. In the Old Testament the brotherhood of all Israelites was emphasized; but in the New Testament the brotherhood in Christ is a relation so much deeper and stronger as to eclipse the other.
Also see definition of "Brotherhood" in Word Study
