The words mol, mole sound the same but have different meanings and spellings. Why do mol, mole sound the same even though they are completely different words?
The answer is simple: mol, mole are homophones of the English language.
Variant of mole5.
A small congenital growth on the human skin, usually slightly raised and dark and sometimes hairy, especially a pigmented nevus.
Any of various small insectivorous mammals of the family Talpidae, usually living underground and having thickset bodies with light brown to dark gray silky fur, rudimentary eyes, tough muzzles, and strong forefeet for burrowing.
A machine that bores through hard surfaces, used especially for tunneling through rock.
A spy who operates from within an organization, especially a double agent operating against his or her own government from within its intelligence establishment.
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").