sir

SIR noun

uk/sɜːr/ us sir noun
(FORMAL LETTER)

B2 You write 'Sir' at the beginning of a formal letter to a man when you do not know his name.

сударь
Dear Sir, I am writing to... Sir
a title used in the UK before the name of a man who has been officially respected or who has a high social rank

сэр
Sir Cliff Richard