The words said, sed sound the same but have different meanings and spellings. Why do said, sed sound the same even though they are completely different words?
The answer is simple: said, sed are homophones of the English language.
To utter aloud; pronounce: The children said, "Good morning.”
To express in words: Say what's on your mind.
To state as one's opinion or judgment; declare: I say let's eat out.
To state as a determination of fact: It's hard to say who is right in this matter.
Past tense and past participle of say.
Law Named or mentioned before; aforementioned: Said party has denied the charges.
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").