The words accidence, accidents sound the same but have different meanings and spellings. Why do accidence, accidents sound the same even though they are completely different words?
The answer is simple: accidence, accidents are homophones of the English language.
The section of morphology that deals with the inflections of words.
Plural form of accident.
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").