Archaic reading of 友; in modern Japanese, 友 is read とも for 'friend'. This reading appears mainly in classical texts or fixed expressions.
See also: 友 (とも)
In old waka poems, 友 is sometimes read as ゆう.
Archaic noun/adjectival noun meaning affection, especially between siblings. Extremely rare; modern equivalents include 兄弟愛 or 愛情.
In classical Japanese, there are examples where 友 expresses affection for siblings.
close friend; best friend
friendship; camaraderie
friendship; friendly relations
friend; companion; acquaintance · friendship; companionship; social relations
comrade in arms; war buddy; fellow soldier
old friend; old pal
fraternity; friendship; brotherly love
sworn friend; close ally
friendly forces; allied army
bad friend; undesirable companion; bad influence · partner in crime; close friend; buddy
school friend; classmate
classmate
yuzen dyeing; yuzen pattern; yuzen silk
friend; companion
friendly nation
schoolmate; alumnus
hemophilia
colleague; workmate; comrade
critical friend; friend who gives frank advice
deceased friend
haiku poetry pals; haiku friends
fellow party member · party supporter; party sympathizer
friendship; friendly relations
association; club; friends of ...
allied political party; friendly party
friend
friendship's responsibilities; duties of friendship
friendship; friendly relations; fellowship
The reading ゆう is an older Sino-Japanese reading (呉音 or 漢音) of 友, largely replaced by とも in modern Japanese. The sibling affection sense is a historical extension of the 'friend' meaning.