Commenting on the theory, popularised by Jerome, that the “brothers” of Jesus were actually cousins or some other form of close relatives, John McHugh wrote:
St. Jerome’s theory as expounded in the Adversus Helvidium cannot stand. Its presentation of the relationships within the Lor's’ family has been demolished by Lightfoot, and in any case Jerome himself abandoned this theory in the end. But even the second strand of his theory (namely, that in the Bible the word ‘brothers’ means ‘cousins’) is to be rejected. It is often said, in support of this theory, that neither Hebrew nor Aramaic has a special word to denote a ‘first cousin’; but they do have a word for ‘uncle’ (dodh: Lev 10:4; Num 34:11 etc.) and for ‘aunt’ (dodhah; Ex 6:20; Lev 20:20), so that a word for ‘cousin’ is not needed, for it is always possible to talk about ‘my uncle’s son’ or ‘the daughter of my aunt’. Moreover, the gospels were written not in Hebrew or Aramaic, but in Hellenistic Greek, which has the very precise word ανεψιος (in the New Testament, only in Col 4:10) and the three rather general words συγγενεια, συγγενης, and συγγενις. It was not for lack of a wider vocabulary that the evangelists wrote about the ‘brothers’ of Jesus.
In the New Testament, the term ‘brothers’ does not mean ‘cousins’. It means ‘brothers’. (John McHugh, The Mother of Jesus in the New Testament [Garden City, N.Y.: Doubleday & Company, Inc., 1975], 253-54, italics in original)
