The words mask, masque sound the same but have different meanings and spellings. Why do mask, masque sound the same even though they are completely different words?
The answer is simple: mask, masque are homophones of the English language.
A facial covering worn for ritual.
A grotesque or comical representation of a face, worn especially to frighten or amuse, as at Halloween.
A covering worn on the face to conceal one's identity, as:
A covering, as of cloth, that has openings for the eyes, entirely or partly conceals the face, and is worn especially at a masquerade ball.
A dramatic entertainment, usually performed by masked players representing mythological or allegorical figures, that was popular in England in the 16th and early 17th centuries.
A dramatic verse composition written for such an entertainment.
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").