The words doc, dock sound the same but have different meanings and spellings. Why do doc, dock sound the same even though they are completely different words?
The answer is simple: doc, dock are homophones of the English language.
Informal A physician, dentist, or veterinarian.
The area of water between two piers or alongside a pier that receives a ship for loading, unloading, or repairs.
A pier; a wharf.
A group of piers on a commercial waterfront that serve as a general landing area for ships or boats. Often used in the plural.
A platform at which trucks or trains load or unload cargo.
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").