The words psychosis, sycosis sound the same but have different meanings and spellings. Why do psychosis, sycosis sound the same even though they are completely different words?
The answer is simple: psychosis, sycosis are homophones of the English language.
A severe mental disorder, with or without organic damage, characterized by derangement of personality and loss of contact with reality and causing deterioration of normal social functioning.
A chronic inflammation of the hair follicles, especially of the beard, characterized by eruption of pimples and nodules.
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").