The words grocer, grosser sound the same but have different meanings and spellings. Why do grocer, grosser sound the same even though they are completely different words?
The answer is simple: grocer, grosser are homophones of the English language.
One that sells foodstuffs and various household supplies.
comparative form of gross: more gross
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.