The words coco, cocoa sound the same but have different meanings and spellings. Why do coco, cocoa sound the same even though they are completely different words?
The answer is simple: coco, cocoa are homophones of the English language.
Coconut, the fruit of the coconut palm.
A powder made from cacao seeds after they have been fermented, roasted, shelled, ground, and freed of most of their fat.
A beverage made by mixing this powder with sugar in hot water or milk.
A moderate brown to reddish brown.
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").