The words mustard, mustered sound the same but have different meanings and spellings. Why do mustard, mustered sound the same even though they are completely different words?
The answer is simple: mustard, mustered are homophones of the English language.
A dark yellow to light olive brown.
Any of various Eurasian plants of the genus Brassica, especially B. nigra and B. juncea, which are cultivated for their pungent seeds and edible leaves.
A condiment made from the powdered seeds of certain of these plants.
A member of the mustard family.
Simple past tense and past participle of muster.
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.