The words hour, our sound the same but have different meanings and spellings. Why do hour, our sound the same even though they are completely different words?
The answer is simple: hour, our are homophones of the English language.
The present time: the man of the hour.
One of the 24 equal parts of a day.
One of the points on a timepiece marking off 12 or 24 successive intervals of 60 minutes, from midnight to noon and noon to midnight or from midnight to midnight.
The time of day indicated by a 12-hour clock.
Used as a modifier before a noun: our accomplishments; our hometown.
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.
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").