The words marquee, marquis sound the same but have different meanings and spellings. Why do marquee, marquis sound the same even though they are completely different words?
The answer is simple: marquee, marquis are homophones of the English language.
A large tent, often with open sides, used chiefly for outdoor entertainment.
A rooflike structure, often bearing a signboard, projecting over an entrance, as to a theater or hotel. Also called marquise.
Being an athlete of exceptional skill and popularity: The team is hoping to sign a marquee player.
A nobleman ranking below a duke and above an earl or a count.
Used as a title for such a nobleman.
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").