The words humorous, humerus sound the same but have different meanings and spellings. Why do humorous, humerus sound the same even though they are completely different words?
The answer is simple: humorous, humerus are homophones of the English language.
The long bone of the arm or forelimb, extending from the shoulder to the elbow.
Full of or characterized by humor; funny: a humorous story.
Employing or showing humor; witty: a humorous writer.
Archaic Given to moods or whims; capricious.
Obsolete Damp; moist.
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.