The words throne, thrown sound the same but have different meanings and spellings. Why do throne, thrown sound the same even though they are completely different words?
The answer is simple: throne, thrown are homophones of the English language.
A chair occupied by an exalted personage, such as a sovereign or bishop, on state or ceremonial occasions, often situated on a dais and sometimes having a canopy and ornate decoration.
A personage who occupies a throne.
The power, dignity, or rank of such a personage; sovereignty.
Christianity The third of the nine orders of angels in medieval angelology.
Past participle of throw.
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").