Latin, senex; Spanish, señor; Italian, signor; French, sicur; Norman, sire; English, sir. According to some, Greek is connected with Sir; on the analogy
of = Latin sum; = Latin semper; = Latin sapa.
(a clerical address). Clergymen had at one time Sir
to their name. This is not the Sir
of knighthood, but merely a
translation of the university word dominus
given to graduates,
Hugh Evans,” etc.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894