友 is one of the most commonly used Japanese kanji, and it also has a lot of special readings in addition to the standard onyomi and kunyomi readings.
ONYOMI 音読み
とも tomo
KUNYOMI 訓読み
ユウ yuu
Examples
まさかの時の友こそ真の友。A friend in need is a friend indeed.類は友を呼ぶ。Birds of a feather will gather together.犬は人間の最良の友です。A dog is a man’s best friend.私と友に眠る。She lies here beside me.彼女は私の誠実な友になった。I found a true friend in her.彼は都合のよい時だけの友だ。He is but a fair weather friend.彼は病気の友を毎日見舞いに来る。He comes to see his sick friend day after day.よい友を選ぶことは大切だ。It is important for us to choose good friends.彼は犬をよき友とした。He found a good companion in his dog.彼は私の主人の腹心の友。He is my boss’s friend and confidant.