The words loaner, loner sound the same but have different meanings and spellings. Why do loaner, loner sound the same even though they are completely different words?
The answer is simple: loaner, loner are homophones of the English language.
one who loans; a lender
something that is frequently loaned
One who avoids the company of other people.
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").