The words hissed, hist sound the same but have different meanings and spellings. Why do hissed, hist sound the same even though they are completely different words?
The answer is simple: hissed, hist are homophones of the English language.
Simple past tense and past participle of hiss.
history, mainly used by schoolchildren.
A sibilant exclamation that one should be silent
Definitions 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").