The words ward, warred sound the same but have different meanings and spellings. Why do ward, warred sound the same even though they are completely different words?
The answer is simple: ward, warred are homophones of the English language.
The state of being under guard; custody.
A division of a city or town, especially an electoral district, for administrative and representative purposes.
A district of some English and Scottish counties corresponding roughly to the hundred or the wapentake.
A room in a hospital usually holding six or more patients.
Simple past tense and past participle of war.
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.
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").