The words pecten, pectin sound the same but have different meanings and spellings. Why do pecten, pectin sound the same even though they are completely different words?
The answer is simple: pecten, pectin are homophones of the English language.
A body structure or organ resembling a comb, as the ridged part of the eyelid of reptiles and birds.
A scallop of the genus Pecten.
Any of a group of water-soluble colloidal carbohydrates of high molecular weight found in ripe fruits, such as apples, plums, and grapefruit, and used to jell various foods, drugs, and cosmetics.
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").