The words conch, conk sound the same but have different meanings and spellings. Why do conch, conk sound the same even though they are completely different words?
The answer is simple: conch, conk are homophones of the English language.
Any of various tropical marine gastropod mollusks, especially of the genera Strombus and Cassis, having large, often brightly colored spiral shells and edible flesh.
The shell of one of these gastropod mollusks, used as an ornament, in making cameos, or as a horn.
Anatomy See concha.
A blow, especially on the head.
The head.
Chiefly British The human nose.
To hit, especially on the head.
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").