The words seraph, serif sound the same but have different meanings and spellings. Why do seraph, serif sound the same even though they are completely different words?
The answer is simple: seraph, serif are homophones of the English language.
A celestial being having three pairs of wings.
Christianity The first of the nine orders of angels in medieval angelology.
A fine line finishing off the main strokes of a letter, as at the top and bottom of M.
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").