The words courier, currier sound the same but have different meanings and spellings. Why do courier, currier sound the same even though they are completely different words?
The answer is simple: courier, currier are homophones of the English language.
An employee of a travel agency serving as a guide for tourists.
A personal attendant hired to make arrangements for a journey.
A spy carrying secret information.
A messenger, especially one on official diplomatic business.
One that prepares tanned hides for use.
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.