The words door, dor sound the same but have different meanings and spellings. Why do door, dor sound the same even though they are completely different words?
The answer is simple: door, dor are homophones of the English language.
A movable structure used to close off an entrance, typically consisting of a panel that swings on hinges or that slides or rotates.
A similar part on a piece of furniture or a vehicle.
The room or building to which a door belongs: They live three doors down the hall.
A large European dung beetle, Geotrupes stercorarius, that makes a droning noise while flying.
General term for flying insect which makes a loud humming noise, such as the June bug or a bumblebee.
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").