The words choc, chock sound the same but have different meanings and spellings. Why do choc, chock sound the same even though they are completely different words?
The answer is simple: choc, chock are homophones of the English language.
short form of chocolate (the food or an individual piece of confectionery)
A block or wedge placed under something else, such as a wheel, to keep it from moving.
Nautical A heavy fitting of metal or wood with two jaws curving inward, through which a rope or cable may be run.
To fit with or secure by a chock: The plane's wheels were chocked and chained down.
Nautical To place (a boat) on chocks.
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").