Final answer:
The term for a single diamond in a setting from the French for 'alone' is solitaire. It's a popular choice for engagement rings and stands out for its singular beauty and representation of uniqueness in a relationship.
Step-by-step explanation:
The term for a single diamond in a setting which is derived from the French word for 'alone' is solitaire. A solitaire setting typically features a single prominent diamond that stands alone, capturing and reflecting light to showcase its brilliance. This setting is often used for engagement rings and symbolizes the unique importance of the relationship it represents.
Unlike solitaire, the terms radiant, marquise, and cushion refer to specific cuts or shapes of diamonds, which can influence their sparkle, but do not pertain to the number of diamonds in a setting. Each diamond cut has unique characteristics: a radiant cut has trimmed corners and is known for its brilliant sparkle, a marquise cut is an elongated shape with pointed ends, and a cushion cut has rounded corners and large facets to increase its luster.