The term 'diamond weight' can be broken down into three crossword solutions: CARAT (5 letters), STONE (5 letters), and Neil (4 letters). A CARAT is a unit of measurement used to weigh diamonds, and is equal to 0.2 grams. A STONE is a unit of measurement used to weigh gemstones, and is equal to 14 pounds. Neil is a reference to Neil Lane, a famous American jewelry designer who has designed engagement rings for many celebrities.