The words sashay, sachet sound the same but have different meanings and spellings. Why do sashay, sachet sound the same even though they are completely different words?
The answer is simple: sashay, sachet are homophones of the English language.
A small packet of perfumed powder used to scent clothes, as in trunks or closets.
To walk or proceed, especially in an easy or casual manner.
To strut or flounce in a showy manner: sashaying around the dinner party in his fancy new clothes.
To perform the chassé in dancing.
To move in a sideways manner.
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").