The words mach, mock sound the same but have different meanings and spellings. Why do mach, mock sound the same even though they are completely different words?
The answer is simple: mach, mock are homophones of the English language.
Mach, Ernst 1838-1916. Austrian physicist and philosopher who played a central role in the development of logical positivism. His works include the influential Science of Mathematics (1883).
An object of scorn or derision.
To treat with ridicule or contempt; deride.
To mimic, as in sport or derision. See Synonyms at ridicule.
To imitate; counterfeit.
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").