The answer to the crossword question “See 21-Down” is “ONE“. This means that the answer to 21-Down is the number “1“. The clue “See” is often used in crosswords to indicate that the answer can be found in another clue. In this case, the answer to 21-Down is related to the number “1“. Overall, the answer is short and simple, but it is important to pay attention to the clues and context in order to solve the crossword puzzle successfully.