The words toughed, tuft sound the same but have different meanings and spellings. Why do toughed, tuft sound the same even though they are completely different words?
The answer is simple: toughed, tuft are homophones of the English language.
Simple past tense and past participle of tough.
A short cluster of elongated strands, as of yarn, hair, or grass, attached at the base or growing close together.
A dense clump, especially of trees or bushes.
To furnish or ornament with tufts or a tuft.
To pass threads through the layers of (a quilt, mattress, or upholstery), securing the thread ends with a knot or button.
Definitions from Wiktionary, Creative Commons Attribution/Share-Alike License, 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").