The words oars, ores sound the same but have different meanings and spellings. Why do oars, ores sound the same even though they are completely different words?
The answer is simple: oars, ores are homophones of the English language.
Plural form of oar.
Third-person singular simple present indicative form of oar.
Plural form of ore.
Definitions 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.