大伯 literally 'big uncle' — in Chinese kinship it specifically means father's oldest brother (
伯 >
父 >
叔 order by age). Outside the family it works like English 'sir' for an older man. Pairs with
大娘 as the gendered respectful forms in rural/northern speech. Not to be confused with
大伯子 (dàbǎizi), which is a wife's term for her husband's older brother.