by Giuseppe Monno
The Greek term adelphós derives from delphýs (“womb”), with a copulative alpha prefixed, and thus etymologically means “of the same womb,” hence “brother.” The Hebrew ’ach is its Semitic equivalent.
In the Septuagint (LXX)—the Greek translation of the Hebrew Scriptures produced for the Jewish diaspora—and in the New Testament, however, adelphós is used in a much broader sense than the narrow meaning of “biological brother.” Let us consider some biblical examples:
Biological brothers
Genesis 4:1–2:
“The man had intercourse with his wife Eve, and she conceived and gave birth to Cain… Next she gave birth to his brother Abel.”
Cain and Abel share the same parents and are therefore brothers in the strict sense.
First cousins
1 Chronicles 23:21–22:
“Sons of Merari: Mahli and Mushi. Sons of Mahli: Eleazar and Kish. Eleazar died without sons, but had daughters; the sons of Kish, their brothers, married them.”
Eleazar and Kish are brothers (both sons of Mahli), but the daughters of Eleazar and the sons of Kish are first cousins; yet the text refers to them as “brothers.”
Uncle and nephew
Genesis 13:8:
“Abram said to Lot, ‘Let there be no quarrel between you and me… for we are brothers.’”
Lot was the son of Haran, Abram’s brother (cf. Genesis 11:27). Thus they were uncle and nephew, yet the term used is “brothers.”
Members of the same tribe
1 Chronicles 15:4–10:
“David assembled the sons of Aaron and the Levites… of the sons of Kohath: Uriel the chief with one hundred and twenty brothers; of the sons of Merari: Asaiah the chief with two hundred and twenty brothers; …”
Here “brothers” refers to members of the same tribal group or clan.
Fellow citizens
Genesis 19:6–7:
“Lot went out to them at the doorway… and said, ‘I beg you, my brothers, do not behave wickedly.’”
Lot addresses the inhabitants of Sodom—his fellow citizens—as “brothers.”
Spouses
Tobit 7:12:
“Raguel replied, ‘I will do so! She is given to you according to the law of Moses… Take her; from now on you are her brother and she your sister.’”
In this context, “brother” and “sister” express the marital bond.
Those in need
Matthew 25:40:
“In truth I tell you, in so far as you did this to one of the least of these brothers of mine, you did it to me.”
Here “brothers” refers to the hungry, the thirsty, the stranger, the naked, the sick, and the imprisoned (cf. Matthew 25:31–46).
Disciples of Christ
John 20:17:
“Jesus said to her, ‘Do not cling to me, because I have not yet ascended to the Father. But go and find the brothers and tell them: I am ascending to my Father and your Father, to my God and your God.’”
Here “brothers” refers to the disciples (v. 18).
Members of the same people
Acts 3:17:
“Now I know, brothers, that neither you nor your leaders had any idea what you were really doing.”
Peter addresses members of his own people as “brothers.”
Those who do the will of God
Matthew 12:49–50:
“Stretching out his hand towards his disciples he said, ‘Here are my mother and my brothers. For anyone who does the will of my Father in heaven, he is my brother and sister and mother.’”
Here Jesus extends the meaning of “brother” to all who do the will of God.
These examples clearly show that adelphós, while originally meaning a biological brother, acquires a wide semantic range in the Greek Bible and the New Testament: it can refer to close relatives, members of the same people, fellow believers, and—at a deeper level—anyone living in communion with God.
Both the Septuagint and the New Testament reflect a thoroughly Semitic mindset. In biblical Hebrew, ’ach (“brother”) does not refer exclusively to a sibling, but can also denote cousins, members of a clan, or those belonging to the same people.
When Jewish scribes translated the Hebrew Scriptures into Greek (LXX), they preserved this Semitic perspective, almost invariably rendering ’ach as adelphós.
In the New Testament, adelphós plays a central role in Christian teaching: it does not merely indicate a relationship of blood, but expresses the reality of a universal brotherhood in Christ (cf. Matthew 12:50). In this sense, it becomes a richly theological term, conveying both communal and spiritual unity.
Although the New Testament is written in Greek, its thought-world remains fundamentally Semitic. The sacred authors adopt the linguistic conventions of the Septuagint, which had already established the norm: ’ach = adelphós, without introducing distinctions typical of Greek usage but foreign to Hebrew thought.
Greek did possess a more specific term for “cousin” (anepsiós), yet the biblical authors use it only rarely. Instead, they follow the Semitic logic and the tradition of the Septuagint, in which adelphós encompasses a much broader range of meaning. This choice is not merely linguistic, but theological, expressing a vision of fraternity that transcends ties of blood.