The words jewel, joule sound the same but have different meanings and spellings. Why do jewel, joule sound the same even though they are completely different words?
The answer is simple: jewel, joule are homophones of the English language.
A precious stone; a gem.
A small natural or artificial gem used as a bearing in a watch.
A costly ornament of precious metal or gems.
One that is treasured or esteemed.
The International System unit of electrical, mechanical, and thermal energy.
A unit of electrical energy equal to the work done when a current of one ampere is passed through a resistance of one ohm for one second.
A unit of energy equal to the work done when a force of one newton acts through a distance of one meter. See Table at measurement.
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.