The words penni, penny sound the same but have different meanings and spellings. Why do penni, penny sound the same even though they are completely different words?
The answer is simple: penni, penny are homophones of the English language.
A copper coin of Finland.
In the United States and Canada, the coin that is worth one cent.
A coin used in Great Britain since 1971, worth 1/100 of a pound. Also called new penny.
A coin formerly used in Great Britain, worth 1/12 of a shilling or 1/240 of a pound.
A coin formerly used in the Republic of Ireland, worth 1/100 of a pound.
Definitions from The Century Dictionary and Cyclopedia, 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").