It seems that the Greek word transliterated 'adelphos' is the relevant word with 'adelphos' being the singular and 'adelphoi' the plural.
The root of this word means 'from the same womb' so denotes membership in the same family. I learned this from 'Thayer's Greek Lexicon'. I've placed the link to this reference below but it was difficult to read so I found another reference that is much simpler. I've placed that link below too.
As a Jehovah's Witness, I was taught that Christ's brothers referred to in MATT 25:40 were a special group of Christians chosen to go to heaven and that I was not one of them nor was almost everyone else in the organisation. The current understanding amongst Jehovah's Witnesses since recent developments, is probably narrower than even that. Most would view Christ's brothers as referring to the seven men on the Governing Body. Such viewpoints are unscriptural. Christ himself told us who his 'brothers' were in MATT 12:47 - 50. (Please read)
This new appreciation for the word 'brothers' as used in the scriptures which includes all those doing God's will, men and women makes me feel so grateful and cared for. Just think! If we are doing God's will and exercising faith in the ransom and striving to live by the righteous standards outlined in the bible, then we are Christ's brothers. So If we are being shunned, ridiculed, mocked or being treated unjustly, Jesus views this as being done to him!
I feel humbled by this realisation as I guess we all feel insignificant at times and yet, these verses which I NEVER EVER thought would apply to me, now comfort me and make me feel precious to Jesus. I always knew that Jehovah loved and cared for me but now I have a new and wonderful understanding of Jesus' protective care too. It's all such a grand privilege.
Our friend Dom rang up the other night as he was doing his bible reading and discovered something amazing!
He noticed in many verses where the New World Translation reads 'brothers', other translations use the term 'brothers and sisters' instead. This difference becomes particularly significant when reading certain scriptures so it is worth learning more. An interlinear translation helps.
I have the 'Kingdom Interlinear Translation of the Greek Scriptures' which is produced by the Watchtower Society and I thought I'd look up a scripture where I knew that the words 'brother' and 'sister' were used separately - MARK 10:29 - 31. See the image below with the two Greek words highlighted.
I then went to MATTHEW 25:40 where Jesus speaks of his brothers and the New World Translation uses the same word, 'brothers' to translate this visibly different word. This made me want to learn more about the Greek word in question .......