The words cent, scent, sent sound the same but have different meanings and spellings. Why do cent, scent, sent sound the same even though they are completely different words?
The answer is simple: cent, scent, sent are homophones of the English language.
See Table at currency.
A distinctive, often agreeable odor. See Synonyms at fragrance, smell.
A perfume: an expensive French scent.
An odor left by the passing of an animal.
The trail of a hunted animal or fugitive.
Past tense and past participle of send1.
See Table at currency.
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").