The words boullion, bullion sound the same but have different meanings and spellings. Why do boullion, bullion sound the same even though they are completely different words?
The answer is simple: boullion, bullion are homophones of the English language.
Gold or silver considered with respect to quantity rather than value.
Gold or silver in the form of bars, ingots, or plates.
A heavy lace trimming made of twisted gold or silver threads.
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").