Main Difference
The main difference between Lord and Sir is that the Lord is a title of nobility for proprietary power and control of a territory given by a King or religious authorities and Sir is a honorific title
Lord
Lord is an appellation for a person or deity who has authority, control, or power over others acting like a master, a chief, or a ruler. The appellation can also denote certain persons who hold a title of the peerage in the United Kingdom, or are entitled to courtesy titles. The collective “Lords” can refer to a group or body of peers.
Sir
Sir is an honorific address used in a number of situations in many anglophone cultures. The term can be used as a formal prefix, especially in the Commonwealth, for males who have been given certain honours or titles (such as knights and baronets), where usage is strictly governed by law and custom.
The term is also commonly used as a respectful way to address a man, usually of superior social status or holding a commissioned military rank. Equivalent terms of address to females are ‘ma’am’ or ‘madam’ in most cases, or in the case of a young woman, girl, or unmarried woman who prefers to be addressed as such, ‘miss’. The equivalent term for a knighted woman or baronetess is Dame, or ‘Lady’ for the wife of a knight or baronet.
Lord (noun)
The master of the servants of a household; the master of a feudal manor
Lord (noun)
The male head of a household, a father or husband.
Lord (noun)
One possessing similar mastery over others; any feudal superior generally; any nobleman or aristocrat; any chief, prince, or sovereign ruler; in Scotland, a male member of the lowest rank of nobility (the equivalent rank in England is baron)
Lord (noun)
The owner of a house, piece of land, or other possession
Lord (noun)
A feudal tenant holding his manor directly of the king
Lord (noun)
A peer of the realm, particularly a temporal one
Lord (noun)
One possessing similar mastery in figurative senses (esp. as lord of ~)
Lord (noun)
A baron or lesser nobleman, as opposed to greater ones
Lord (noun)
The heavenly body considered to possess a dominant influence over an event, time, etc.
Lord (noun)
A hunchback.
Lord (noun)
Sixpence.
Lord (verb)
Domineer or act like a lord.
Lord (verb)
To invest with the dignity, power, and privileges of a lord; to grant the title of lord.
Sir (noun)
A man of a higher rank or position.
Sir (noun)
A respectful term of address to a man of higher rank or position, particularly:
Sir (noun)
to a knight or other low member of the peerage.
“Just be careful. He gets whingy now if you don’t address him as Sir John.”
Sir (noun)
to a superior military officer.
“Sir, yes sir.”
Sir (noun)
A respectful term of address to any male, especially if his name or proper title is unknown.
“Excuse me, sir, do you know the way to the art museum?”
Sir (noun)
Used as an intensifier after yes or no.
“Sir, yes sir.”
Sir (verb)
To address (someone) using “sir”.
“Sir, yes, sir!
Don’t you sir me, private! I work for a living!”