The words caddie, caddy, cadi sound the same but have different meanings and spellings. Why do caddie, caddy, cadi sound the same even though they are completely different words?
The answer is simple: caddie, caddy, cadi are homophones of the English language.
One hired to serve as an attendant to a golfer, especially by carrying the golf clubs.
Scots A boy who does odd jobs.
Any of various devices for moving, carrying, or holding an item or collection of items, especially:
A lightweight wheeled cart, often fitted with shelves or racks.
A small container, such as a box, used especially for holding tea.
A container for storing a group of items not in use.
Computer Science A protective case used to load a CD-ROM into a disk drive.
Variant of caddie.
Alternative form of qadi.
Definitions from The American Heritage® Dictionary of the English Language, 4th Edition, from Wiktionary, Creative Commons Attribution/Share-Alike License and Wordnik.
Homophones (literally "same sound") are usually defined as words that share the same pronunciation, regardless of how they are spelled.