The words sail, sale sound the same but have different meanings and spellings. Why do sail, sale sound the same even though they are completely different words?
The answer is simple: sail, sale are homophones of the English language.
Nautical The sails of a ship or boat.
Nautical A piece of fabric sewn together and fitted to the spars and rigging of a vessel so as to convert the force of the wind into forward motion of the vessel.
Nautical To voyage upon or across: sail the Pacific.
Nautical The superstructure of a submarine.
The exchange of goods or services for an amount of money or its equivalent; the act of selling.
An instance of selling.
An opportunity for selling or being sold; demand.
Availability for purchase: a store where pets are for sale.
Definitions from The American Heritage® Dictionary of the English Language, 4th Edition and Wordnik.
Homophones (literally "same sound") are usually defined as words that share the same pronunciation, regardless of how they are spelled.