伯父さん
おじさん · ojisan · JLPT N2 · noun
gentleman
伯 = eldest sibling + 父 = father: an elder father, so uncle (おじさん)
伯 originally marks the eldest or senior sibling, so 伯父 names a father's elder brother. The polite おじさん is also used for any middle-aged gentleman, as in 'Excuse me, sir.'