The words higher, hire sound the same but have different meanings and spellings. Why do higher, hire sound the same even though they are completely different words?
The answer is simple: higher, hire are homophones of the English language.
comparative form of high: more high
comparative form of high: more high
The act of hiring.
The condition or fact of being hired.
Payment for services; wages.
To engage the services of (a person) for a fee; employ: hired a new clerk.
Definitions from Wiktionary, Creative Commons Attribution/Share-Alike License, 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").