The words magnate, magnet sound the same but have different meanings and spellings. Why do magnate, magnet sound the same even though they are completely different words?
The answer is simple: magnate, magnet are homophones of the English language.
A powerful or influential person, especially in business or industry: an oil magnate.
An object that is surrounded by a magnetic field and that has the property, either natural or induced, of attracting iron or steel.
An electromagnet.
A person, a place, an object, or a situation that exerts attraction.
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.
If they are spelled the same then they are also homographs (and homonyms); if they are spelled differently then they are also heterographs (literally "different writing").