The words premier, premiere sound the same but have different meanings and spellings. Why do premier, premiere sound the same even though they are completely different words?
The answer is simple: premier, premiere are homophones of the English language.
First in status or importance; principal or chief: an architect of premier rank.
First to occur or exist; earliest.
A prime minister.
A chief administrative officer, as of a Canadian province.
The first public performance, as of a movie or play.
To present the first public performance of.
To have the first public performance.
To make a first appearance in a public performance.
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.