The words envoi, envoy sound the same but have different meanings and spellings. Why do envoi, envoy sound the same even though they are completely different words?
The answer is simple: envoi, envoy are homophones of the English language.
Variant of envoy2.
A representative of a government who is sent on a special diplomatic mission.
A minister plenipotentiary assigned to a foreign embassy, ranking next below the ambassador.
A messenger; an agent.
A short closing stanza in certain verse forms, such as the ballade or sestina, dedicating the poem to a patron or summarizing its main ideas.
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").