The words loan, lone sound the same but have different meanings and spellings. Why do loan, lone sound the same even though they are completely different words?
The answer is simple: loan, lone are homophones of the English language.
Something lent for temporary use.
A sum of money lent at interest.
An act of lending; a grant for temporary use: asked for the loan of a garden hose.
A temporary transfer to a duty or place away from a regular job: an efficiency expert on loan from the main office.
Without accompaniment; solitary: a lone skier on the mountain.
Without companionship; isolated or lonely.
Being the only one; sole: the lone doctor in the county.
Situated by itself: a lone tree on the prairie; a lone blue tile in a white floor.
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").