The words throe, throw sound the same but have different meanings and spellings. Why do throe, throw sound the same even though they are completely different words?
The answer is simple: throe, throw are homophones of the English language.
A severe pang or spasm of pain, as in childbirth. See Synonyms at pain.
A condition of agonizing struggle or trouble: a country in the throes of economic collapse.
To propel through the air with a motion of the hand or arm.
To discharge into the air by any means: a machine that throws tennis balls; ash that was thrown by an erupting volcano.
To hurl or fling with great force or speed: threw themselves on the food; jetsam that had been thrown up onto the shore.
To force (an opponent) to the ground or floor, as in wrestling or the martial arts.
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").