sir

1 ENTRIES FOUND:
sir /ˈsɚ/ noun
plural sirs
sir
/ˈsɚ/
noun
plural sirs
Britannica Dictionary definition of SIR
1 
[noncount]
a  — used without a name as a form of polite address to a man you do not know — compare ma'am, madam, miss
b  — used without a name as a form of polite address to a man of rank or authority (such as a military or police officer, teacher, or master)
2 
Sir [count] — used without a name as a form of address at the beginning of a formal letter
3 
Sir [noncount] — used as a title before the name of a knight or baronet
4 
[noncount] US, informal — used in the phrases no sir and yes sir for emphasis, to show surprise, etc.