Is it permissible, linguistically and Islamically, to describe a brother as a friend if he has been befriended with affection and mercy, and what is the evidence for that?

In language, friendship (sadaqa) means sincerity of affection and advice. This is a description that can be applied to both close and distant relations. It is permissible to describe a brother as a friend if he is characterized by sincerity of affection and devotion in offering advice. The general principle in Islamic law is permissibility unless there is evidence to prohibit something.