A brother (pl.: brothers or brethren) is a man or boy who shares one or more parents with another; a male sibling. The female counterpart is a sister. Although the term typically refers to a familial relationship, it is sometimes used endearingly to refer to non-familial relationships. A full brother is a first degree relative. Overview. The term brother comes from the Proto-Indo-European *bʰréh₂tēr, which becomes Latin frater, of the same meaning. Sibling warmth or affection between male siblings has been correlated to some more negative effects.
https://en.wikipedia.org/wiki/Brother