The words cygnet, signet sound the same but have different meanings and spellings. Why do cygnet, signet sound the same even though they are completely different words?
The answer is simple: cygnet, signet are homophones of the English language.
A seal, especially one used officially to mark documents.
The impression made with such a seal.
To mark or endorse with a signet.
The ring-shaped form of the Plasmodium of malaria. See <internalXref urlencoded="signet-ring">signet-ring</internalXref>, 2.
Definitions , from The American Heritage® Dictionary of the English Language, 5th Edition., from The Century Dictionary. 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").