The words stanch, staunch sound the same but have different meanings and spellings. Why do stanch, staunch sound the same even though they are completely different words?
The answer is simple: stanch, staunch are homophones of the English language.
To stop or check the flow of (blood or tears, for example).
To stop the flow of blood from (a wound).
To stop, check, or allay: "My anxiety is stanched; I am at peace” ( Scott Turow). See Usage Note at staunch1.
Variant of staunch1. See Usage Note at staunch1.
Firm and steadfast; true. See Synonyms at faithful.
Having a strong or substantial construction or constitution.
Variant of stanch1. See Usage Note at staunch1.
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").