The words guise, guys sound the same but have different meanings and spellings. Why do guise, guys sound the same even though they are completely different words?
The answer is simple: guise, guys are homophones of the English language.
Outward appearance or aspect; semblance.
False appearance; pretense: spoke to me under the guise of friendship.
Mode of dress; garb: huddled on the street in the guise of beggars.
Obsolete Custom; habit.
Plural form of guy.
Persons, irrespective of their genders.
A form of address for a group of male persons or a group of mixed male and female persons.
Definitions from The American Heritage® Dictionary of the English Language, 4th Edition, from Wiktionary, Creative Commons Attribution/Share-Alike License and Wordnik.
Homophones (literally "same sound") are usually defined as words that share the same pronunciation, regardless of how they are spelled.