The words clack, clacque sound the same but have different meanings and spellings. Why do clack, clacque sound the same even though they are completely different words?
The answer is simple: clack, clacque are homophones of the English language.
To make an abrupt, sharp sound, as in the collision of two hard surfaces.
To chatter thoughtlessly or at length.
To cackle or cluck, as a hen.
To cause to make an abrupt, sharp sound.
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").