The words pocks, pox sound the same but have different meanings and spellings. Why do pocks, pox sound the same even though they are completely different words?
The answer is simple: pocks, pox are homophones of the English language.
Plural form of pock.
A disease such as chickenpox or smallpox, characterized by purulent skin eruptions that may leave pockmarks.
Syphilis.
Archaic Misfortune and calamity.
Definitions from Wiktionary, Creative Commons Attribution/Share-Alike License, 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").