The words cot, khat sound the same but have different meanings and spellings. Why do cot, khat sound the same even though they are completely different words?
The answer is simple: cot, khat are homophones of the English language.
A narrow bed, especially one made of canvas on a collapsible frame.
Chiefly British A crib.
A small house.
A protective covering or sheath.
An evergreen shrub (Catha edulis) native to tropical East Africa, having dark green opposite leaves that are chewed fresh for their stimulating effects.
A tealike beverage prepared from the leaves of this plant.
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").