The words grisly, grizzly sound the same but have different meanings and spellings. Why do grisly, grizzly sound the same even though they are completely different words?
The answer is simple: grisly, grizzly are homophones of the English language.
Inspiring repugnance; gruesome. See Synonyms at ghastly.
Grayish or flecked with gray.
A grizzly bear.
Definitions 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.