An archaic reading (yuu) of 友 meaning 'friend' or 'companion' in classical/literary contexts.
昔の詩に『我が友(ゆう)あるを喜べ』とある。
An old poem says, 'Rejoice that I have a friend (yuu).'
旅路で出会った一人の友(ゆう)が助けてくれた。
One friend (yuu) I met on the journey helped me.
An archaic adjectival/nounal use expressing affectionate feelings toward siblings (a kind of familial affection).
兄に対する友(ゆう)を忘れぬ者こそ家を守る者なり。
Those who do not forget affection (yuu) toward their elder brother are the ones who uphold the family.