This is a cross-reference clue - the definition and/or wordplay are found by looking at clue 1 in the puzzle grid.
You need to examine clue 1 to find either the definition for this answer or the letters/words that will help construct MONDRIAN. The cross-reference 'See 1' indicates that clue 1 contains the key information needed to solve this clue.
Answer: MONDRIAN | This cross-reference clue requires looking at clue 1 in the puzzle to find the definition or wordplay that leads to MONDRIAN, the famous Dutch abstract painter known for his geometric compositions.