A Grief Observed – C. S. Lewis (1961)
Marriage is diversifying in this day and age from the concept it raised in years gone by. It is no longer the sole domain of religion with regards to the union of a man and a woman, but in many countries, it now encompasses civil ceremonies and same sex unions. As such it could be argued that the definition of the term wife has broadened.
The person you choose to live your life with should not only be your partner and lover, but also take on the role of care giver, confidant, nurse, teacher, pupil, friend, shipmate through the storms, companion, ally, alter ego, colleague, collaborator, soul-mate, and in some cases even your rival.
As to the term brother, this tends these day to be taken literally, as in a male sibling within a family but another connotation is that of comrade, someone that will stand by you at all times regardless of the situation.
Therefore, I feel the old-fashioned definition is a better description of what a partner should be, whether it be connected to a marriage or not and is not restricted to the woman.