The words sics, six sound the same but have different meanings and spellings. Why do sics, six sound the same even though they are completely different words?
The answer is simple: sics, six are homophones of the English language.
Third-person singular simple present indicative form of sic.
The cardinal number equal to 5 + 1.
The sixth in a set or sequence.
Something having six parts, units, or members, especially a motor vehicle having six cylinders.
at sixes and sevens In a state of confusion or disorder.
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").